Emission and occupational health risk assessment of harmful contaminants in various processes in a typical semiconductor manufacturing industry building

Abstract

Workers in semiconductor factories have occupational health risks from exposure to chemical substances. This work analyzed hazardous chemical substances in the key process of a semiconductor factory in China, and studied cancer and non-cancer health risks and occupational health risks of workers. Research results show that more than half of the processes contain compounds such as hydrogen fluoride, chlorine, hydrogen chloride, ammonia and 2-propanol, and their concentrations vary greatly depending on the process. The occupational exposure index (Ei) of some processes is greater than 1, which means that there are adverse occupational health risks, including wet etching (WETCH), physical vapour deposition (PVD), furnace process (FUR), chemicals storehouse (CS) and diffusion (from inspection area). The pollutants with a high contribution rate to E_i vary with the process, and WETCH (operating area) has the highest contribution rate of sulphuric acid (93.33%). The Hazard Quotient (HQ_i) of PVD and CS is far greater than 1, indicating that there is a non-cancer risk. The lifetime cancer risk (LCR_i) of wastewater treatment and CS is greater than 10⁻⁴, which indicates a risk of cancer. The General Engineer has higher health risks than the Duty Engineer due to the higher exposure frequency.

Keywords

Occupational health risk Cancer risk assessment Non-cancer risk assessment Harmful contaminants

Introduction

As a modern chemical-intensive industry, semiconductor manufacturing has become one of the industries with the most serious occupational diseases.¹ The working environment of workers involves physical hazards (noise, power frequency electric field) and chemical hazardous agents (Organic solvent, acids, alkalis, metals and their compounds, of which chemical hazards are accounted for a large proportion.^2–7 These harmful chemicals can damage multiple organ systems such as the respiratory tract, cardiovascular system and nervous system, and cause cancer and skin damage.^8–16 Workers working in semiconductor factories may be exposed to chemical hazards that can cause occupational diseases.

Some studies have analyzed specific pollutants in semiconductors and found that although the exposure levels of most pollutants are lower than the current exposure limit,^17,18 individual pollutants (gallium, indium and arsenic) have adverse effects on the health of workers.^19,20 In addition, some scholars have studied the occupational health risks of workers exposed to photolithography process,^17,21,22 and the wastewater treatment.^23–25 The occupational health risks faced by workers in semiconductor factories vary due to the types of pollutants and processes, and a comprehensive evaluation and analysis are required.

According to the measurement data of the working environment in the past, more than 98% of the concentration of harmful contaminants evaluated in the semiconductor factory are below the current occupational exposure limits (OELs), and the concentration of most chemical substances are below than 50% of the OELs.^2,4,26 In fact, due to the wide variety of semiconductor raw materials and the complex production process, workers are exposed to a variety of pollutants. Therefore, it is impossible to confirm whether workers have adverse health effects based on specific chemical hazards lower than OELs. Some scholars have concluded that the cumulative health risk value of each process in industries such as recycling workshops and oil refineries is much greater than a single pollutant.^27,28 For factories with complex processes, the cumulative health risks can provide a more comprehensive view of workers’ occupational health risks. However, there are few comprehensive assessments of occupational health risks in the semiconductor industry, mainly for protecting state-of-the-art technology,²⁹ resulting in the lack of sufficient hard data on the current pollutant levels in semiconductor factories. Therefore, it is urgent to conduct a comprehensive assessment of the pollutant levels of the key processes of semiconductor factories and the occupational health risks of workers.

Based on previous findings, the occupational exposure risk research of workers mostly adopts the recommended threshold limit value (TLV) by American Conference of Government Industrial Hygienists (ACGIH),³⁰ and there are also studies adopting the occupational health standards recommended by the other two organizations, namely, Occupational Safety and Health Administration (OSHA)³¹ and National Institute for Occupational Safety and Health (NIOSH).^32,33 The occupational thresholds provided by these three institutions are actually different, and there is no relevant comparison and research on how to choose amongst them for occupational health risk assessment in the semiconductor industry.

In this study, we carried out field harmful contaminants measurement in a semiconductor factory from one of the top ten factories in China, in order to understand the harmful contaminants emission data from different specific processes in the semiconductor factories and to investigate the process-specific characteristics of harmful contaminants pollution and their consequent health risks. The research covers most of the key processes of semiconductors, including operating processes and inspection processes. The operating processes include photolithography (LITHO), diffusion (DIFF), etching (ETCH) and thin film deposition (TF). There are a total of 27 kinds of pollutants, including metals and their compounds, acids, bases and volatile organic compounds (VOCs). U.S. Environmental Protection Agency (US EPA) standard methods are used to assess the potential health risks of chemical pollutants,³⁴ including cancer and non-cancer risks. Occupational exposure cancer risk is assessed using methods of the US Centers for Disease Control and Prevention (US CDC). The threshold limit values used in the assessment were from four institutions such as ACGIH, OSHA, NIOSH and China Occupational Exposure Limits (COEL).^31–33,35 The comprehensive assessment of the carcinogenic risk caused by occupational exposure of semiconductor workers is of importance to the workers and the industry.

Materials and methods

Study design

This study selected a top 10 semiconductor factory in China with an annual output of about 400,000 chips. From 5 to 9 November 2018, hazardous pollutants were sampled at the location of the main processing equipment of the specific process, covering most of the key processes of the semiconductor factory. Figure 1 shows simplified flow charts including the specific operation processes, where samples were collected for each working zone in the chip industry.

According to the type of operation, the workflow is divided into operation processes and inspection processes. The operation processes include photolithography (LITHO), diffusion (DIFF), etching (ETCH) and thin film deposition (TF). The DIFF processes include furnace process (FUR), ion implantation (IMP) and rapid thermal processing (RTP). The ETCH processes include wet etching (WETCH) and dry etching (DETCH). The TF processes include chemical mechanical polishing (CMP), physical vapour deposition (PVD) and chemical vapour deposition (CVD). There are production process inspection (PPI), waste gas/wastewater treatment (WG/WW), chemicals storehouse (CS) and power equipment area (PE) in inspection area. In order to distinguish the processes throughout this article, processes that are not marked as inspection areas belong to the operating area.

Sample collection and analysis

The major chemical occupational hazards involved in semiconductor factories are fluorides, hydrogen fluoride, chlorine, nitrogen dioxide and hydrochloric acid. Table 1 lists the species of chemical substances and their sampler detection limits, collected air volume, measurement methods and references^36–53 in this study, and Table 2 shows specification, applicable and scope of the devices. In this study, for each process (Figure 1), representative workplaces were selected for air sampling, including the workplaces with the highest concentration of harmful substances in the air and the longest exposure time for workers.

Table 1.

The species of chemical substances and their sampler, detection limits, collected air volume, measurement methods and references in this study.

Chemical substances	Sampler	Detection limit (mg/m³)	Collected air volume (L)	Measurement methods	Reference
Acetic acid	Activated carbon adsorption tube	0.32	4.5	Solvent desorption-gas chromatography	GBZ/T 300.112, 2017³⁷
Acetone	Activated carbon adsorption tube	0.37	1.5	Solvent desorption-gas chromatography	GBZ/T 300.103, 2017³⁸
Arsenic	Millipore filter	4.9 × 10⁻⁵	45	Atomic absorption spectrometry	GBZ/T 300.47, 2017³⁹
Arsine	Millipore filter	0.03	15	Diethyl dithiocarbamate spectrophotometric	GBZ/T 300.47, 2017³⁹
Ammonia	Absorbent solution	0.13	7.5	Nessler’s reagent spectrophotometry	GBZ/T 160.29, 2004⁴⁰
Boron trifluoride	Absorbent solution	1	15	Mandelic acid spectrophotometry	GBZ/T 300.35, 2017⁴¹
n-Butyl acetate	Activated carbon adsorption tube	0.27	1.5	Solvent desorption-gas chromatography	GBZ/T 160.63, 2004⁴²
Carbon monoxide	Instrument direct reading	0.1	/	Non-dispersive infrared gas analyzer	GBZ/T 300.37, 2017⁴³
Chlorine	Absorbent solution	0.02	7.5	Methyl orange spectrophotometric method	GBZ/T 160.37, 2004⁴⁴
Cyclohexanone	Activated carbon adsorption tube	0.32	1.5	Solvent desorption-gas chromatography	GBZ/T 160.56, 2004⁴⁵
Fluorides	Glass fibre filter	0.01	75	Ion selective electrode method	GBZ/T 160.36, 2004⁴⁶
Hydrogen chloride	Absorbent solution	0.48	7.5	Ion chromatography	GBZ/T 160.37, 2004⁴⁴
Hydrogen fluoride	Absorbent solution	0.01	75	Ion chromatography	GBZ/T 160.36, 2004⁴⁶
Hydrogen peroxide	Absorbent solution	0.8	15	Titanyl sulphate spectrophotometry	GBZ/T 300.48, 2017⁴⁷
Hydrogen sulphide	Absorbent solution	0.3	7.5	Silver nitrate colorimetry	GBZ/T 160.33, 2004⁴⁸
Methane	Air bag	0.09	/	Direct injection-gas chromatography	HJ 604, 2017⁴⁹
Methanol	Activated carbon adsorption tube	0.59	1.5	Thermal desorption-gas chromatography	GBZ/T 300.84, 2017⁵⁰
Nitric oxide	Absorbent solution	0.0024	10	Ethylene diamine dihydrochloride spectrophotometric method	GBZ/T 160.29, 2004⁴⁰
Nitrogen dioxide	Absorbent solution	0.02	7.5	Ethylene diamine dihydrochloride spectrophotometric method	GBZ/T 160.29, 2004⁴⁰
Ozone	Absorbent solution	0.02	7.5	Eugenol spectrophotometry	GBZ/T 300.48, 2017⁴⁷
Phosphine	Absorbent solution	0.03	15	Ammonium molybdate spectrophotometry	GBZ/T 160.30, 2004⁵¹
Phosphoric acid	Absorbent solution	0.1	7.5	Ammonium molybdate spectrophotometry	GBZ/T 160.30, 2004⁵¹
2-Propanol	Activated carbon adsorption tube	0.26	1.5	Solvent desorption-gas chromatography	GBZ/T 300.84, 2017⁵⁰
Sodium hydroxide	Millipore filter	0.0046	75	Flame atomic absorption spectrometry	GBZ/T 300.22, 2017⁵²
Sulphur dioxide	Absorbent solution	0.1	7.5	Pararosaniline hydrochloride spectrophotometry	GBZ/T 160.33, 2004⁴⁸
Sulphur hexafluoride	Air bag	0.0014	/	Direct injection-gas chromatography	GBZ/T 300.51, 2017⁵³
Sulphuric acid	Absorbent solution	0.2	75	Ion chromatography	GBZ/T 160.33, 2004⁴⁸

Table 2.

Specification, applicable and scope of the devices.

No.	Device name	Specification	Manufacturer or brand	Applicable scope
1	PH meter	PHSJ-5	REX	(−2.000∼18.000) pH
2	Portable visible spectrophotometer	DR2800	HACH	340–900 nm
3	Portable visible spectrophotometer	DR1900	HACH	340∼800 nm
4	Gas chromatograph	GC-2010A	Shimadzu	/
5	Colorimetric tube with stopper	/	Bomex	10 mL
6	Portable infrared gas analyzer	GXH-3010/3011AE	Huayun	0–200.0 × 10⁻⁶ CO, 0–1.000% CO₂
7	Atomic absorption spectrometer	AA240FS	Varian	185∼900 nm
8	Air sampler	QC-2	Beijing Municipal Institute of Labour Protection	0.1–1.2 L/min
9		Omni5000 IS	Yancheng Fangyuan Protection Technology Co., Ltd.	5–5000 mL/min
10		ZC-Q	Zhejiang Hengda Instrumentation Co., Ltd.	0–5.0 L/min
11		QC-4	Beijing Municipal Institute of Labour Protection	0.1–1.5 L/min

A total of three occupational exposure limit concentrations were detected, including the TLV-TWA (time-weighted average) concentration representing an 8-h workday within a 40-h workweek, the TLV-STEL (short-term exposure limit) concentration for a 15-min TWA exposure that should not be exceeded at any time during a workday and the TLV-C (Ceiling) concentration that should not be exceeded during any part of the working exposure. For most substances, it is very important to apply TWA alone or together with STEL. For certain substances (such as irritating gases), only TLV-C is applicable. Therefore, sampling and analysis were carried out according to the existing TLVs of chemical hazardous agents in GBZ 2.1.³⁵

The specific operation steps of on-site sampling were carried out according to GBZ 159-2004.³⁶ Sampling of hazardous chemical substances was carried out on the breathing belt at the operating position of the worker, and the sampling point was set in the downwind direction of the worker’s workplace. It was far away from the exhaust outlet and the area where vortex may be generated. During the sampling period, workers were working normally and the production floor remained in full operation. The temperature and atmospheric pressure at the sampling point are shown in Table 3. The sampling time was 15 min, and the sampling instruments include atmospheric sampler (QC-2, Beijing Municipal Institute of Labour Protection, China), explosion-proof air sampler (QC-4, Beijing Municipal Institute of Labour Protection, China), atmospheric sampler (ZC-Q, Zhejiang Hengda Instrumentation Co. Ltd., China) and atmospheric sampler (Airchek52, SKC).

Table 3.

Environmental conditions of sampling sites.

Sampling date	Temperature (°C)	Atmospheric pressure
5 November 2018	22–25	100.0
6 November 2018	22–25	102.2
7 November 2018	15–28	101.9
8 November 2018	18–25	100.7
9 November 2018	24–25	100.8

Quality assurance and quality control

All instruments and equipment in this study had been calibrated to ensure accurate monitoring. While air samples were taken, one parallel sample was analyzed for every ten samples and each sample has a field blank. The relative deviation of the target in parallel samples should be less than or equal to 5%. The blank control sample must go through the same process (including field exposure, transportation, storage and laboratory analysis) and procedures as the sample to reduce systematic errors. All detected compounds and their method detection limits (MDLs) are listed in Table 1.

Non-cancer and cancer risks assessment using the US EPA method

Long-term exposure of workers to harmful chemical substances may cause health risks of cancer or other toxic effects (non-cancer). As workers wear work clothes and rubber gloves, the risk of skin exposure and oral intake is low, so this paper focuses on the assessment of workers' inhalation health risks.²⁶ The method recommended by the US EPA was used to assess non-cancer and cancer risk of chemicals via inhalation.^34,54,55

In addition, the lifetime cancer risk associated with compound i (LCR_i) was assessed using equation (1)³⁴:

L C R_{i} = C_{i} \times 1000 \times U R_{i}

(1)

where C_i is the mass concentration of compound i (mg/m³, from TLV-TWA in the study), UR_i (unit risk: (μg/m³)⁻¹) is an estimation of the increased cancer risk from inhalation exposure to a 1 μg/m³ of compound i for a lifetime. The UR_i values of the compound are taken from the Integrated Risk Information System (IRIS), Agency for Toxic Substances and Disease Registry (ATSDR), California Office of Environmental Health Hazard Assessment (OEHHA), US EPA Health Impact Assessment Summary Table (HEAST) or US EPA Provisional Value provisional values (PPRTV).^56–60 For the TLV of the different institutions, the latest data are given priority. Table 4 lists the UR_i values used in this study and their sources.

Table 4.

The inhalation cancer potency factor, unit risks and non-cancer reference concentrations of the chemical substances found in this study.^56–60

Chemical substances	Non-cancer		Chemical substances	Non-cancer
Chemical substances	RfC (μg/m³)	Source	Chemical substances	RfC (μg/m³)	Source
Acetic acid	—	—	Hydrogen sulphide	2.00 × 10⁻³	IRIS
Acetone	3.10	ATSDR	Methane	—	—
Arsenic	1.50	OEHHA	Methanol	2.00	IRIS
Arsine	5.00 × 10⁻⁵	IRIS	Nitric oxide	—	—
Ammonia	0.50	IRIS	Nitrogen dioxide	—	—
Boron trifluoride	1.30 × 10⁻²	HEAST	Ozone	—	—
n-Butyl acetate	—	—	Phosphine	3.00 × 10⁻⁴	IRIS
Carbon monoxide	—	—	Phosphoric acid	1.00 × 10⁻²	IRIS
Chlorine	1.50 × 10⁻⁴	ATSDR	2-Propanol	0.20	HEAST
Cyclohexanone	0.70	HEAST	Sodium hydroxide	—	—
Fluorides	1.30 × 10⁻²	OEHHA	Sulphur dioxide	—	—
Hydrogen chloride	2.00 × 10⁻²	IRIS	Sulphur hexafluoride	—	—
Hydrogen fluoride	1.40 × 10⁻²	OEHHA	Sulphuric acid	1.00 × 10⁻³	OEHHA
Hydrogen peroxide	—	—	—	—	—
Cancer
Chemical substances	SF (mg/kg/day)⁻¹		Source	UR(μg/m³)⁻¹	Source
Arsenic	1.20		OEHHA	4.30 × 10⁻³	IRIS

Abbreviations: ATSDR (Agency for Toxic Substances and Disease Registry, Centres for Disease Control and Prevention (US CDC));⁵⁷ IRIS (Integrated Risk Information System, US EPA);⁵⁶ HEAST (Health Effects Assessment Summary Tables, US EPA);⁵⁹ OEHHA (Office of Environmental Health Hazard Assessment); RfC (reference dose for chronic oral exposure);⁵⁸ SF: slope factor (SF of styrene obtained from United States Environmental Protection Agency’s Cumulative Exposure Project, others from IRIS).

Compounds with an LCR value greater than 1 × 10⁻⁴ are regarded as ‘identified risks’, between 1 × 10⁻⁵ and 1 × 10⁻⁴ regarded as ‘probable risks’, between 1 × 10⁻⁶ and 1 × 10⁻⁵ regarded as ‘possible risk’, less than 1 × 10⁻⁶ regarded as ‘negligible risk’.⁶¹

The non-cancer risk indicator is expressed by hazard quotient (HQ), which can be given by equation (2). The EC can be given as equation (3).³⁴

H Q_{i} = \frac{E C_{i}}{R F C}

(2)

E C_{i} = \frac{C_{i} \times E T \times E F \times E D}{A T \times 365 \times 24}

(3)

where RFC is chronic inhalation reference concentration (mg/m³); ET is the exposure time (h/week); EF represents the exposure frequency (week/year); ED is the exposure duration (year); AT is average lifetime. Table 4 lists the RFC values used in this study and their sources.^56–60

The values of AT (72.4 years) were taken from China’s human exposure parameters.⁶² There are two main types of workers in semiconductor factories, namely, operators and inspection workers. Operators are divided into general engineer and duty engineer. The daily exposure time (ET) of the two is 8 h (5 days a week) and 11 h (four shifts and two operations, meaning two shifts in 4 days). The inspector has a daily exposure time (ET) of 4 h (5 days a week). The exposure frequency (EF) of the general engineer from operators and the inspector are 250 days, after deducting 104 statutory holidays and 11 statutory holidays. The exposure frequency (EF) of the duty engineer is 171 days, after deducting 11 statutory holidays. The exposure duration (ED) of worker is usually calculated as 35 years.

Tables 4 and 5 summarize inhalation cancer potency factor, unit risks, non-cancer reference concentrations of the chemical substances found and parameters used for the LCR and HQ estimation.

Table 5.

Parameters used for the LCR and HQ estimation.

Parameters	ED (year)	EF for operators (day/year)		ET (h/day)			AT⁶¹ (year)
Parameters	ED (year)	General engineer of operators and inspector	Duty engineer of operators	General engineer of operators	Duty engineer of operators	Inspector	AT⁶¹ (year)
Values	35	250	171	8	11	4	72.4

ED: the exposure duration; EF: the exposure frequency; ET: the exposure time; AT: average lifetime.

For a given toxic chemical substance in the air, when the non-carcinogenic risk HQ is greater than 1, long-term exposure could cause non-carcinogenic health hazards, and HQ < 1 means a safe level.⁶³

Risk assessment for occupational exposure using the ACGIH method

The ACGIH method was used to assess the cancer risk of semiconductor factory workers exposed to harmful substances.^30–33,35 There are three types of OELs, namely, TLV-TWA, TLV-STE and TLV-C. For most substances, there is only TWA or both TWA and STEL. Some substances (such as irritating gases) have only a threshold limit-the upper limit (C). If it exceeds any type of TLVs, the substance is considered to be potentially hazardous.^{30–33,35,64} According to the hazardous substance data in this study and the TLVs list in Table 6, equations (4)–(6) were used to calculate the occupational exposure index (E_i):

E_{T W A_{i}} = \sum_{i}^{n} \frac{C_{i}}{T L V - T W A_{i}}

(4)

E_{S T E L_{i}} = \sum_{i}^{n} \frac{C_{i}}{T L V - S T E L_{i}}

(5)

E_{C_{i}} = \sum_{i}^{n} \frac{C_{i}}{T L V - C_{i}}

(6)

where C_i (mg/m³) is the concentration of compound i. TLV-TWA_i, TLV-STEL_i and TLV-C_i values (mg/m³) are provided by American Conference of Governmental Industrial Hygienists (ACGIH),³⁰ National Institute for Occupational Safety and Health (NIOSH) standard, Occupational Safety³³ and Health Administration (OSHA)³¹ and the China Occupational Exposure Limits (COEL).³⁵ In the microenvironment, compounds with E_i higher than 1.0 are considered to pose potential health risks to workers.

Table 6.

Average concentration of compounds detected during semiconductor manufacturing.

Chemical substances	LITHO	DIFF			ETCH		TF			PPI			WG/WW		CS	PE
Chemical substances	LITHO	FUR	IMP	RTP	WETCH	DETCH	CMP	PVD	CVD	DIFF	ETCH	TF	WG	WW	CS	PE
(a) C_TWA (unit: mg/m³)
Fluorides	2 × 10⁻³	2 × 10⁻³	3 × 10⁻³	/	/	1.58 × 10⁻²	/	/	5.2 × 10⁻³	2.17 × 10⁻³	1.47 × 10⁻³	1.67 × 10⁻³	1.49 × 10⁻³	2 × 10⁻³	9.14 × 10⁻⁴	1 × 10⁻³
Chlorine	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Phosphine	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Nitrogen dioxide	/	2 × 10⁻³	/	/	/	/	/	/	3 × 10⁻³	/	2 × 10⁻³	0.02	4 × 10⁻⁴	/	1.1 × 10⁻²	1 × 10⁻⁴
Nitric oxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	0.004	/
Hydrogen fluoride	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Hydrogen chloride	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Sulphuric acid	/	/	/	/	0.2	/	/	0.2	/	/	/	/	/	/	0.124	/
Boron trifluoride	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Hydrogen peroxide	/	/	/	/	0.1	/	0.03	0.1	/	/	/	/	/	/	0.39	0.39
Ammonia	/	0.17	/	/	0.3	/	0.2	/	1.26	0.5	/	0.25	7.83 × 10⁻²	/	0.18	0.19
Ozone	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Sulphur dioxide	/	/	/	/	/	0.1	/	/	/	/	0.06	/	0.1	/	7.33 × 10⁻²	/
Phosphoric acid	/	/	/	/	/	/	/	/	/	/	/	/	/	0.01	0.14	/
Hydrogen sulphide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Methanol	0.32	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Cyclohexanone	0.41	/	/	/	/	/	/	/	/	/	/	/	/	/	0.17	/
2-Propanol	0.26	/	/	/	0.26	/	0.26	/	/	/	/	/	0.26	/	0.26	0.26
Acetone	0.37	/	/	/	/	/	/	/	/	/	/	/	0.37	/	0.43	/
Carbon monoxide	/	/	/	/	/	/	/	/	/	/	0.01	/	0.02	/	0.02	1 × 10⁻³
Acetic acid	/	/	/	/	/	/	/	/	/	/	/	/	/	/	0.19	/
Methane	/	/	/	/	/	Undetected	/	/	/	/	Undetected	/	/	/	/	Undetected
Sulphur hexafluoride	/	/	/	/	/	1.4 × 10⁻³	/	/	/	/	1.4 × 10⁻³	/	/	/	1.4 × 10⁻³	/
n-Butyl acetate	Undetected	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Arsine	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Arsenic	/	/	/	/	/	/	/	/	/	/	/	/	/	2.5 × 10⁻⁵	0.05	/
Sodium hydroxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
(b) C_STEL (unit: mg/m³)
Fluorides	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Chlorine	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Phosphine	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Nitrogen dioxide	/	4 × 10⁻³	/	/	/	/	/	/	3 × 10⁻³	/	4 × 10⁻³	0.02	0.1	/	0.08	0.1
Nitric oxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	0.01	/
Hydrogen fluoride	/	/	/	/	/	/	/	/	/	/	/	/	/	/	0.7	/
Hydrogen chloride	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Sulphuric acid	/	/	/	/	0.2	/	/	0.2	/	/	/	/	/	/	0.24	/
Boron trifluoride	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Hydrogen peroxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Ammonia	/	1	/	/	1.5	/	1.8	/	5.39	4.4	/	3.95	3.43	/	1.68	1.5
Ozone	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Sulphur dioxide	/	/	/	/	/	0.28	/	/	/	/	0.25	/	0.1	/	0.27	/
Phosphoric acid	/	/	/	/	/	/	/	/	/	/	/	/	/	0.25	0.18	/
Hydrogen sulphide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Methanol	/	0.59	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Cyclohexanone	0.59	/	/	/	/	/	/	/	/	/	/	/	/	/	0.17	/
2-Propanol	0.26	/	/	/	0.26	/	0.26	/	/	/	/	/	0.26	/	0.26	/
Acetone	0.37	/	/	/	/	/	/	/	/	/	/	/	0.37	/	0.425	/
Carbon monoxide	/	/	/	/	/	/	/	/	/	/	0.6	/	1.2	/	0.41	0.6
Acetic acid	/	/	/	/	/	/	/	/	/	/	/	/	/	/	0.19	/
Methane	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Sulphur hexafluoride	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
n-Butyl acetate	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Arsine	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Arsenic	/	/	/	/	/	/	/	/	/	/	/	/	/	2.8 × 10⁻⁵	0.05	/
Sodium hydroxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
(c) CC (unit: mg/m3)
Fluorides	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Chlorine	/	0.13	/	/	/	0.1	/	/	/	0.1	0.15	/	0.2	/	3.6 × 10⁻²	/
Phosphine	/	0.09	0.1	/	/	/	/	/	/	0.09	/	/	/	/	6.5 × 10⁻³	/
Nitrogen dioxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Nitric oxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Hydrogen fluoride	/	2.2 × 10⁻²	/	/	0.03	0.03	0.03	/	/	0.02	0.01	/	/	/	0.02	/
Hydrogen chloride	/	1.74	/	0.68	1.55	/	/	/	/	/	/	0.53	0.67	/	0.66	0.48
Sulphuric acid	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Boron trifluoride	/	/	0.04	/	/	2.5 × 10⁻²	/	/	/	/	0.02	/	0.02	/	/	/
Hydrogen peroxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Ammonia	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Ozone	/	/	/	/	/	/	/	/	/	0.1	0.02	0.02	0.02	/	/	/
Sulphur dioxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Phosphoric acid	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Hydrogen sulphide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	0.3
Methanol	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Cyclohexanone	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
2-Propanol	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Acetone	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Carbon monoxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Acetic acid	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Methane	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Sulphur hexafluoride	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
n-Butyl acetate	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Arsine	/	/	9 × 10⁻³	/	/	/	/	/	/	0.06	/	/	/	/	3 × 10⁻³	/
Arsenic	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/	/
Sodium hydroxide	/	/	/	/	/	/	/	/	/	/	/	/	/	/	0.1	0.02

Subscript: TWA: time-weighted average; STEL: short-term exposure limit; C: ceiling.

Results and discussion

General emission characteristics

According to the existing threshold limits of hazardous chemical substances in the Chinese standard GBZ 2.1,³⁵ this study tested the hazardous chemical substances in semiconductor factories, including its corresponding TLV-TWA, TLV-C or TLV-STEL. The chemical hazardous substances and their average concentrations of the main processes are shown in Table 6. Table 6 shows the various processes of the semiconductor industry that involve the use of potentially hazardous chemicals in the working environment, such as metal and their compound, organic solvents, acids and toxic gases. Methane and n-Butyl acetate were not detected because the actual concentration was lower than the minimum detection concentration of the equipment.

The chemical substances in the air could vary due to different processes. There is more than one hazardous chemical substance in every process. Amongst them, the CS has the most types of pollutants, including fluorides, nitrogen dioxide, nitrogen monoxide and sulphuric acid. In semiconductor factories, almost half of the processes contain compounds such as fluoride, hydrogen fluoride, chlorine, nitrogen dioxide, chlorine, ammonia and 2-propanol. However, some hazardous chemical substances, including nitric oxide, boron trifluoride, sulphuric acid, ozone, phosphoric acid, hydrogen sulphide, methanol, cyclohexanone, acetic acid, n-Butyl acetate and arsine have only been detected in a few processes. For example, nitric oxide is only in the CS, methanol in the LITHO, hydrogen sulphide in the PE and arsine in the IMP and CS.

The concentrations of these compounds could vary with different processes. The ratio of compound concentration in different processes ranged from 1 to 1786. Amongst them, the average of TWA of nitrogen dioxide in FUR was 0.02 mg/m³, and the average of TWA in PE was 0.0001 mg/m³ and the ratio of the two was 200. Therefore, we should focus on the nitrogen dioxide concentration level of FUR. In addition, the ratio of STEL concentration of sulphur hexafluoride was 1786, and the ratio of STEL concentration of ammonia was 333. To sum up, the concentration levels of the same chemical substance in different processes are different and should be explained independently according to the process.

In summary, the equipment and chemical reagents used in their workplaces are different because of the difference in processes, resulting in differences in the types and concentration levels of chemical pollutants. Therefore, this may lead to differences in the occupational risks of workers exposed to different process environments, and it is not comprehensive to study the occupational health risks of workers exposed to certain pollutants or specific processes only. We should conduct differentiated analysis based on different processes and set corresponding protective measures according to the types of chemical substances.

Non-cancer and lifetime cancer risk assessment

Figure 2 shows the non-cancer health risk value (HQ) of hazardous chemical substances in different processes in a semiconductor factory. The three processes of IMP, WETCH and CVD in the operation area are not subject to inhalation cancer and non-cancer health risk assessments because workers wear self-contained respirators.

The results in Figure 2 show that the HQ value of a general engineer was generally higher than that of a duty engineer, indicating that general engineers in semiconductor factories have a higher non-cancer health risk. The reason is that a general engineer has a higher exposure frequency (EF) than a duty engineer.

Figure 2 shows that the HQ values of the general engineer and duty engineer exposed to the PVD were 22.07 and 20.76, respectively. The HQ value of the inspector in the CS was 7.74. The HQ value is far greater than the safety threshold of 1, which indicates that there is an unfavourable non-cancer health risk for workers. Therefore, workers exposed to the process of PVD and CS need to consider their occupational health risks. The HQ value of other processes is much smaller than the threshold value 1, including 11 processes such as LITHO, FUR, DETCH and CMP.

However, due to the limitations of current research, the toxicity mechanisms of some pollutants have not been grasped by relevant international organizations, resulting in their RFC values not being updated, such as nitrogen dioxide, nitric oxide, hydrogen peroxide and ozone. Therefore, the HQ calculated in this study may be lower than the actual value.

In this study, the cancer health risk value of inhalation of arsenic was calculated only for workers’ exposure in the WW and CS. This is because the parameter (SF or UR) for quantitative estimate of carcinogenic risk from inhalation exposure have not been assessed under the IRIS and other Program. The calculated LCR value ranged from 4.30 × 10⁻⁶ to 2.11 × 10⁻⁴, and the average value was 1.08 × 10⁻⁴. The average value of LCR was greater than 1 × 10⁻⁴, so the WW is considered to be an ‘identified risk’. The average value of LCR in the CS was 0.22, which is far greater than 1 × 10⁻⁴, so this process is considered a ‘determined risk’.

Occupational exposure health risk assessment

In order to obtain a more comprehensive view of the occupational health risks of semiconductor factories, the E_i value was calculated based on five thresholds, including ACGIH, NIOSH, OSHA and COEL, min (ACGIH, NIOH, OSHA and COEL). The min (ACGIH, NIOH, OSHA and COEL) means to take the minimum of the reference values of ACGIH, NIOSH, OSHA and COEL as the threshold limit.

Figure 3 shows the E_i calculated based on min (ACGIH, NIOH, OSHA and COEL). For the E_TWA value of a single chemical substance in Figure 3, the sulphuric acid in the WETCH and PVD were 1 and 1, respectively, and arsenic in the CS was 5. These values all exceeded the threshold 1, which means that there is an occupational health risk. For the E_STEL value, arsenic in the CS was 25, far exceeding 1, which means a high occupational health risk. Other chemical hazardous substances were less than the threshold limit, indicating that the occupational health risks to workers are small or negligible.

Although the E_i value of a single chemical substance in most semiconductor factories was less than 1 (Figure 3), there was more than one pollutant for a certain process, resulting in differences in the cumulative occupational risk (E_i) of each process. The E_TWA value of WETCH, PVD and CS was 1.09, 1.07 and 6.12, respectively. The E_STEL in the CS was 25.85. The E_C values of FUR and DIFF in the inspection area were 1.03 and 1.11, respectively. There are occupational health risks. Therefore, there are occupational health risks in the WETCH, PVD, FUR, CS and DIFF of inspection area.

Figure 4 compares the E_i values calculated using the five TLVs including ACGIH, NIOSH, OSHA, COEL and min (ACGIH, NIOSH, OSHA and COEL). For ACGIH, the E_TWA of WETCH, PVD and CS is 1.08, 1.07 and 6.09, respectively. For NIOSH, the E_STEL of the CS was 25.33. For OSHA, the E_TWA of the CS was 5.57. For COEL, the E_TWA of the CS and the E_STEL of the CS, were 5.58 and 2.78, respectively. The cumulative value of occupational health risk (E_i) varies amongst different institutions because of different TLVs.

In order to clarify the contribution of pollutants in each process to occupational health risks, the proportion of pollutants in each process to E_i was calculated, as shown in Figure 5. Figure 5 shows the contribution rate of pollutants for processes with occupational health risks (E_i ≥1) when using TLVs of min (ACGIH, NIOSH, OSHA and COEL) to calculate. When using TLVs-TWA, the WETCH (operation area) has the largest contribution rate of sulphuric acid (93.33%), followed by hydrogen peroxide (6.56%), ammonia (1.53%) and 2-Propanol (0.07%) contributed the least. Other process contributions rate includes PVD (sulphuric acid and hydrogen peroxide) and CS (arsenic, sulphuric acid and hydrogen peroxide). When using TLVs-STEL, in the CS, the contribution ratio of chemical substances is arsenic, sulphur dioxide in order. When TLVs-C are used for risk assessment, the contribution rate of pollutants includes FUR (hydrogen chloride, phosphine and chlorine), and the DIFF of inspection area (ozone, phosphine, arsine and chlorine).

In summary, for different processes, the chemical substances that contribute to the occupational health risk are different.

Comparison with other research and national standards

Table 7 shows the comparison of the results with other reported research and national standards. Table 7 shows that the occupational exposure limit standards used in previous studies are mostly come from the recommended values formulated by organizations such as ACGIH, NIOSH, OSHA and mandatory standards established by various countries or regions. The concentration level of most single chemical substances is lower than the occupational exposure limit of various institutions,^{2,4,19,21,26,65} which is similar to this study. More than 93% of the chemical substances are below the occupational exposure limit. However, in this study, there are still some pollutants above the occupational exposure limit, such as the sulphuric acid in the WETCH and PVD, and arsenic in the CS.

Table 7.

Comparison with other researches and national standards.

Country or region	The historical industrial air sampling data
Korea: Historical exposure data compiled from 2012 through 2014²	Routine exposures of operators and maintenance workers < OELs
Ion implantation workers¹⁹	Arsenic concentration: Operators < OELs < maintenance engineers
Korea: Four photolithography processes at three different semiconductor manufacturing factories²¹	VOCs concentrations in the photolithography processes < 5% of the ACGIH TLVs
US: Approximately 60,000 sample measurements of > 60 chemicals⁴	1978–1986 year: 98.7% < OELs 1987–1997 year: 99.8% < OELs 1998–2004 year: 99.8% < OELs
China:²⁶	Ammonia, chlorine, fluoride, sulphuric acid, hydrogen chloride, ethylene glycol, phosphine, boron trifluoride, isopropanol, benzene and xylene: HQ > 1; < COEL TLVs
Korea: 9 representative wafer fabrication bays⁶⁵	Various chemical substances < KOEL, OSHA, ACGIH and NIOSH TLVs

There are also differences in the health risks for different types of workers. Some scholars have found that maintenance workers exposed to arsine have higher occupational health risks than operating tools.¹⁹ In this study, there are similar conclusions. In other words, compared with the duty engineer, the general engineer in semiconductor factories have a higher non-cancer health risk.

In addition, previous studies have shown that the concentration of pollutants in semiconductor factories is mostly less than TLVs of the institutions, such as, OSHA,³¹ ACGIH,³⁰ NIOSH³³ and COEL;³⁵ that is, there is no occupational health risk. However, the process in the semiconductor factory in this study has occupational health risks, such as WETCH, PVD, FUR CS and DIFF (the inspection area), no matter what, the basis is one of institution (ACGIH, NIOSH, OSHA and COEL). This is because the target of occupational health risk assessment in previous research is a single chemical substance while this research is the cumulative risk value of all chemical substances in the process. The reason is that for workers, their workplace is exposed to more than one chemical substance.

In this study, there are differences in the application of TLVs of different institutions for occupational health risk assessment. There are two main reasons for this difference. The first reason is that the TLVs set by different institutions are different. ACGIH, NIOSH and OSHA are the main occupational health standards in the United States of America, and their purposes and basis are different. TLVs established by OSHA are required to be enforced. The TLV standard formulated by ACGIH is updated fastest, but it is a TLV of academic interest. OSHA’s PEL standard is the slowest to update, resulting in the lack of corresponding threshold limits for most chemical substances, and the existing threshold limits are higher than ACGIH. The value of COLE mainly refers to ACGIH. With the deepening of the understanding of harmful factors, many limits of TLVs have been decreasing year by year. As a result, ACGIH’s TLVs values are mostly lower than those of other institutions. The second reason is the lack of TLVs for certain chemicals in these four organizations.

Therefore, for industrial occupational health risk assessment, it is recommended to conduct a comprehensive assessment based on the TLVs of multiple institutions. In addition, most of the pollutant concentrations in semiconductor factories in previous studies were lower than the occupational exposure limits of institutions. However, many processes in semiconductor factories studied in this paper have occupational health risks, such as WETCH, PVD, FUR CS and DIFF (the inspection area).

Conclusion

Workers in semiconductor factories have occupational health risks from chemical exposure. This research conducted detection and analysis of chemical hazardous agents in a number of key processes in a semiconductor factory in China and studied the inhaled cancer and non-cancer health risks, and the occupational health risks of workers.

The research results show that there are many types of chemical substances in each process of a semiconductor factory, and the concentration varied greatly depending on the process, and the ratio ranged from 1 to 1786. The inhalation health risk assessment showed that the HQ value of the general engineer was higher than that of the duty engineer due to the higher exposure frequency. The HQ of physical vapour deposition and chemical substance storage areas is far greater than the safety threshold 1, indicating a non-cancer risk. The LCR of the wastewater area is greater than 10⁻⁴, and there is a health risk of cancer.

93% of the compounds are less than the occupational exposure limit, except for the sulphuric acid (in the WETCH and PVD) and arsenic (in the CS). Furthermore, the cumulative occupational exposure limit E_i of some processes is greater than 1, which means that there may be unfavourable occupational health risks, for example, the WETCH, PVD, FUR, CS and DIFF (the inspection area).

To sum up, the contribution of pollutants to occupational health risks in each process is different, and the research on each kind of pollutants in semiconductor factories should be analyzed in combination with their processes. In addition, the occupational health risks of workers exposed to semiconductor factories cannot be ignored, especially the generation of new pollutants in semiconductor factories due to technology update. Due to the different occupational exposure limit standards of the indicators of various institutions, there are differences in the occupational health risk assessment of workers, which should be comprehensively assessed. ACGIH can be referenced first due to its fast update.

Footnotes

Authors’ contributions

All authors contributed equally in the preparation of this manuscript.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Key Research and Development Program of China (Grant No. 2018YFC0705300).

ORCID iD

Zhichao Wang

References

Bailar

3rd Greenberg

Harrison

LaDou

Richter

Watterson

Trades Union Congress. Santa Clara County Center for Occupational Safety and Health and Silicon Valley Toxics Coalition . Cancer risk in the semiconductor industry: a call for action. Int J Occup Environ Health 2002; 8: 163–168.

Choi

Yoon

Kim

Jeong

Kim

Shin

Park

. Comprehensive evaluation of hazardous chemical exposure control system at a semiconductor manufacturing company in South Korea. Int J Environ Res Public Health 2018; 15: 1162–1214.

Hawkinson

Korpela

. Bolmen RABTSSH. Norwich, USA: William Andrew Publishing, 1998, pp. 187–203.3 - Chemical hazards in semiconductor operations

Marano

Boice

JDJ

Munro

Chadda

Williams

McCarthy

Kivel

Blot

McLaughlin

. Exposure assessment among US workers employed in semiconductor wafer fabrication. J Occup Environ Med 2010; 52(11): 1075–1081.

Hewitt

. Occupational health in metal arc welding. Indoor Built Environ 1996; 5(5): 253–262.

Perez

Frank

Zimmerman

. Health effects associated with organic dust exposure during the handling of municipal solid waste. Indoor Built Environ 2006; 15: 207–212.

Chisholm

. Respirable dust and respirable silica concentrations from construction activities. Indoor Built Environ 1999; 8: 94–106.

Lee

Kim

Park

Kang

. Cancer mortality and incidence in Korean semiconductor workers. Saf Health Work 2011; 2(2): 135–147.

McElvenny

Darnton

Hodgson

Clarke

Elliott

Osman

. Investigation of cancer incidence and mortality at a Scottish semiconductor manufacturing facility. Occup Med (Chic Ill) 2003; 53(7): 419–430.

10.

Park

. Review for Retrospective Exposure Assessment Methods Used in Epidemiologic Cancer Risk Studies of Semiconductor Workers: Limitations and Recommendations. Saf Health Work 2018; 9(3): 249–256.

11.

Darnton

Wilkinson

Miller

MacCalman

Galea

Shafrir

Shafrir2

Cherrie

McElvenny

Osman

. A further study of cancer among the current and former employees of national semiconductor (UK) Ltd., Greenock. Merseyside, UK: health and safety executive and Institute of occupational medicine United Kingdom, https://www.hse.gov.uk/statistics/pdf/repapp2010.pdf (2010, accessed 1 July 2021.

12.

Xue

Zhao

Chi

Yin

Xuan

Wang

. Mutagenicity, health risk, and disease burden of exposure to organic micropollutants in water from a drinking water treatment plant in the Yangtze River Delta, China. Ecotoxicol Environ Saf 2021; 221: 112421.

13.

Zheng

Hou

Wang

Sun

. Health risk assessment of heavy metals in street dust around a zinc smelting plant in China based on bioavailability and bioaccessibility. Ecotoxicol Environ Saf 2020; 197: 110617.

14.

Murithi

Cao

. Increase associated risk of gynaecological cancer due to long-term exposure to high concentration of atmospheric SO₂ industrial pollutant. Indoor Built Environ 2022; 31(8): 2183–2192.

15.

Dong

Xie

. Surveillance for the effects of Carbon Monoxide on health in a tianjin gas factory. Indoor Built Environ 1997; 6(6): 358–361.

16.

Iwegbue

C M A

Nwose

Egobueze

F E

Odali

E W

Tesi

G O

Nwajei

G E

Martincigh

B S

. Risk assessment of human exposure to potentially toxic metals in indoor dust from some small and medium scale enterprise workplace environments in southern Nigeria. Indoor Built Environ 2019; 29: 1137–1154.

17.

Paustenbach

. Assessment of the developmental risks resulting from occupational exposure to select glycol ethers within the semiconductor industry. J Toxicol Environ Health 1988; 23(1): 29–75.

18.

Woskie

Hammond

Hines

Hallock

Kenyon

Schenker

. Personal Fluoride and solvent exposures, and their determinants, in semiconductor manufacturing. Appl Occup Environ Hyg 2000; 15(4): 354–361.

19.

Park

Yang

Jeong

Choi

Kim

Yoon

Park

Paek

. A comprehensive review of arsenic levels in the semiconductor manufacturing industry. Ann Occup Hyg 2010; 54: 869–879.

20.

Chen

. Exposure and health risk of gallium, indium, and arsenic from semiconductor manufacturing industry workers. Bull Environ Contam Toxicol 2007; 78: 123–127.

21.

Park

S-H

Shin

J-A

Park

H-H

G Y

Chung

K-J

Park

H-D

Kim

K-B

Lee

I-S

. Exposure to volatile organic compounds and possibility of exposure to by-product volatile organic compounds in photolithography processes in semiconductor manufacturing factories. Saf Health Work 2011; 2(3): 210–217.

22.

Lee

Yoon

Lee

Jung

Dong

. Retrospective exposure assessment on the photolithography process in semiconductor manufacturing facility. Occup Environ Med 2014; 71(Suppl 1): A70.

23.

Brenner

Neu-Baker

Caglayan

Zurbenko

. Occupational exposure to airborne nanomaterials: an assessment of worker exposure to aerosolized metal oxide nanoparticles in semiconductor wastewater treatment. J Occup Environ Hyg 2015; 12(7): 469–481.

24.

Shepard

Brenner

. Cutaneous exposure scenarios for engineered nanoparticles used in semiconductor fabrication: a preliminary investigation of workplace surface contamination. Int J Occup Environ Health 2014; 20(3): 247–257.

25.

Shepard

Brenner

. An occupational exposure assessment for engineered nanoparticles used in semiconductor fabrication. Ann Occup Hyg 2014; 58: 251–265.

26.

Cai

Zhang

. Occupational health risk assessment in the electronics industry in china based on the occupational classification method and EPA model. Int J Environ Res Public Health 2018; 15(10): 2061.

27.

Chen

Huang

Zhang

. Pollution characteristics and health risk assessment of volatile organic compounds emitted from different plastic solid waste recycling workshops. Environ Int 2015; 77: 85–94.

28.

Zhang

Yan

Gao

Thai

Wang

Chen

Zhou

Gong

Morawska

Wang

. Emission and health risk assessment of volatile organic compounds in various processes of a petroleum refinery in the Pearl River Delta, China. Environ Pollut 2018; 238: 452–461.

29.

Yoon

. Much Concern but Little Research on Semiconductor Occupational Health Issues. J Korean Med Sci 2012; 27(5): 461–464.

30.

ACGIH . American conference of governmental industrial Hygienists: 2017 TLVs and BEIs: threshold limit values for chemical sub-stances and physical agents and biological exposure indices. Cincinnati, OH: ACGIH, 2017, https://www.acgih.org/ (accessed 1 July 2021.

31.

OSHA Occupational Safety and Health Administration . OSHA regulations, https://www.osha.gov/ (2007, accessed 1 July 2021.

32.

Key

. National Institute for occupational safety and health. Encycl Toxicol 2014; 41(8): 454–455.

33.

NIOSH . The national Institute for occupational safety and health, https://www.cdc.gov/niosh/topics/chemical.html (2021, accessed 1 July 2021.

34.

US EPA . Air toxics risk assessment reference library. Technical Resource Manual www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library (2004, accessed 1 July 2021.

35.

GBZ 2.1, 2019 . Occupational Exposure Limits for Hazardous Agents in the Workplace — Part 1: Chemical Hazardous Agents. Beijing: National Health Commission of the People's Republic of China, 2019.

36.

GBZ 159, 2004 . Specifications of Air Sampling for Hazardous Substances Monitoring in the Workplace. Beijing: Ministry of Health of the PRC, 2004.

37.

GBZ/T 300.112, 2017 . Determination of Toxic Substances in Workplace air: Part 112: Formic Acid and Acetic Acid. Beijing: National Health Commission of the People's Republic of China, 2017.

38.

GBZ/T 300.103, 2017 . Determination of Toxic Substances in Workplace Air: Part 103: Acetone, Methyl Ethyl Ketone and Methyl Isobutyl Ketone. Beijing: National Health Commission of the People's Republic of China, 2017.

39.

GBZ/T 300.47, 2017 . Determination of Toxic Substances in Workplace air: Part 47: Arsenic and its Inorganic Compounds. Beijing: National Health Commission of the People's Republic of China, 2017.

40.

GBZ/T 160.29 , 2004. Methods for Determination of Inorganic Nitrogen Compounds in the Air Workplace. Beijing: National Health Commission of the People's Republic of China, 2004.

41.

GBZ/T 3. 00.35, 2017 . Determination of Toxic Substances in Workplace air: Part 35: Boron Trifluoride. Beijing: National Health Commission of the People's Republic of China, 2017.

42.

GBZ/T 160.63, 2004 . Methods for Determination of Saturated Aliphatic Esters in the Air of Workplace. Beijing: National Health Commission of the People's Republic of China, 2004.

43.

GBZ/T 300.37, 2017 . Determination of Toxic Substances in Workplace air: Part 37: Carbon Monoxide and Carbon Dioxide. Beijing: National Health Commission of the People's Republic of China, 2017.

44.

GBZ/T 160.37, 2004 . Methods for Determination of Chlorides in the Air of Workplace. Beijing: National Health Commission of the People's Republic of China, 2004.

45.

GBZ/T 160.56, 2004 . Methods for Determination of Cyclic and Aromatic Ketones in the Air of Workplace. Beijing: National Health Commission of the People's Republic of China, 2004.

46.

GBZ/T 160.36, 2004 . Methods for Determination of Fluorides in the Air of Workplace. Beijing: National Health Commission of the People's Republic of China, 2004.

47.

GBZ/T 300.48, 2017 . Determination of Toxic Substances in Workplace Air: Part 48: Ozone and Hydrogen Peroxide. Beijing: National Health Commission of the People's Republic of China, 2017.

48.

GBZ/T 160.33, 2004 . Methods for Determination of Sulfides in the Air of Workplace. Beijing: National Health Commission of the People's Republic of China, 2004.

49.

HJ 604, 2017 . Ambient air-Determination of Total Hydrocarbons, Methane and Nonmethane Hydrocarbons-Direct Injection/Gas Chromatography. Beijing: Ministry of Environmental Protection, 2017.

50.

GBZ/T 300.84, 2017 . Determination of Toxic Substances in Workplace Air: Part 84: Methyl Alcohol, Propyl Alcohol and Octyl Alcohol. Beijing: National Health Commission of the People's Republic of China, 2017.

51.

GBZ/T 160.30, 2004 . Methods for Determination of Inorganic Phosphorus Compounds in the air of Workplace. Beijing: National Health Commission of the People's Republic of China, 2004.

52.

GBZ/T 300.22, 2017 . Determination of Toxic Substances in Workplace Air: Part 22: Sodium and its Compounds. Beijing: National Health Commission of the People's Republic of China, 2017.

53.

GBZ/T 300.51, 2017 . Determination of Toxic Substances in Workplace Air: Part 51: Sulfur Hexafluoride. Beijing: National Health Commission of the People's Republic of China, 2017.

54.

Roy

Lyou

Kim

Lee

Park

. Commuters health risk associated with particulate matter exposures in subway system – Globally. Build Environ 2022; 216: 109036.

55.

Bai

Wang

. Health risk assessment of heavy metals and poly-aromatic hydrocarbons in particulate matter adsorbed by indoor air purifiers. Indoor Built Environ 2022; 31(6): 1594–1612.

56.

US EPA . Integrated risk information system (IRIS), https://cfpub.epa.gov/ncea/iris_drafts/AtoZ.cfm (2021, accessed 1 July 2021.

57.

ATSDR . US. Agency for toxic substances and disease Registry, www.nano.gov/ATSDR (2021, accessed 1 July 2021.

58.

OEHHA . California Office of environmental health hazard assessment, https://oehha.ca.gov/air/chemicals (2021, accessed 1 July 2021.

59.

US EPA . Health effects assessment summary Tables (heast), http://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=2877 (2021, accessed 1 July 2021.

60.

US EPA . Provisional peer-reviewed toxicity values (PPRTVs), https://www.epa.gov/pprtv (2021, accessed 1 July 2021.

61.

van der Kuijp

Yuan

Huang

. A review of soil heavy metal pollution from mines in China: pollution and health risk assessment. Sci Total Environ 2014; 468-469: 843–853.

62.

Zhao

Duan

. Exposure factors handbook of Chinese population ((Adults). 1st ed.. Beijing: China Environmental Science Press, 2013, pp. 15–17. pp.270–272, pp.748–750, pp.798–799.

63.

Environmental Protection Agency . Office of emergency and remedial response. risk assessment guidance for superfund (RAGS) Part A. Saúde Pública 1989; 804: 636–640.

64.

Zhang

Yan

Gao

Thai

Wang

Chen

Zhou

Gong

Morawska

Wang

. Emission and health risk assessment of volatile organic compounds in various processes of a petroleum refinery in the Pearl River Delta, China. Environ Pollut 2018; 238: 452–461.

65.

Park

Jang

Shin

. Quantitative exposure assessment of various chemical substances in a wafer fabrication industry facility. Saf Health Work 2011; 2: 39–51.