Chemical pollutants in the respiratory zone of welders: Determination of concentrations and hazard analysis

Abstract

BACKGROUND:

Welding pollutants have potentially dangerous effects on the health of welders. Analysis of exposure risks is an appropriate method for industrial hygiene occupational exposure.

OBJECTIVE:

The present study aimed to determine the concentrations of exposure and risk evaluation of welders to fumes and gases in three common types of welding including Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW) and Gas Tungsten Arc Welding (GTAW).

METHODS:

This cross-sectional study was carried out at a steel company. Samples were taken from manganese, chromium and nickel fumes with NIOSH 7300 method and for NO, NO2, CO and O3 gases using direct reading instruments. SQRCA method was used to assess the level of exposure risk.

RESULTS:

Our study showed that the highest and lowest concentrations of exposure to gases were observed in MIG and GTAW welding, respectively. Also, the highest and lowest concentrations of exposure to metals were observed in SMAW and GTAW processes, respectively. Mean exposure to M, Cr and Ni metals was 2.302, 3.195, and 1.241 mg/m³, respectively. Also, mean exposure to CO, NO, NO2 and O3 was 43.05, 27.88, 4.30, and 0.41 ppm, respectively. Results of risk analysis showed that O3, NO2 and Cr had high and very high risk levels in all welding processes.

CONCLUSIONS:

MIG and SMAW welders have a high occupational exposure to metal and toxic gases in welding. Preventive measures such as assessment of workplace air, installation of the ventilation systems, and providing appropriate respiratory protection devices for welders should be taken.

Keywords

Risk assessment fume gas steel industry welders

1 Introduction

The welding process is available in most small and large workplaces and is used to repair problematic parts [1]. The use of welding has increased in recent years. Welding is defined as the process of connecting two pieces of metal to each other by metal melting called the electrode. There are different types of welding. In the process of Shielded Metal Arc Welding (SMAW), a coalescence of metals are produced by heating them with an arc between a covered metal electrode and the work [2]. The SMAW process is popular in the industry because it is cheap, can boil most of the metals and alloys, and can be easily implemented in harsh environments [3].

In the process of Gas Metal Arc Welding (GMAW) and Gas Tungsten Arc Welding (GTAW), shielding of the arc and the molten welded metal is obtained by gas and is used to shield the arc welding to prevent weld contamination by air. Welding of GMAW is a metal bonding process in which the arc between electrode wires is continuous and usable and the metal is welded. The arc is protected from atmospheric pollutants through shielding gases such as carbon dioxide, argon, and helium. The welding current, arc voltage and welding speed are the main variables in each GMAW process [4].

Occupational exposure is greatest with the GTAW process because it creates smaller nanoparticles in comparison to other welding methods. In addition, GTAW is one of the most popular welding methods in various industrial fields, such as the automotive industry [5]. In 2003, Kou reported that this technique allows the operator more control over welding as compared with other welding processes, and leads to very clean, robust, and better quality welding [6].

According to the Business Perspective Guide 2014-2015 published by the US Department of Labor and the US Census Bureau, approximately 500,000 full-time welders work in the USA [7]. There are over 2,000,000 workers globally. In Europe, approximately 730,000 full-time welders work and there are 5,500,000 welding-related jobs [8]. One of the main factors to which a welder is exposed is fume and gas from welding operations. The source of about 90% of the contaminating compounds is the welding consumable and about 10% is the base metal [9].

The gases produced during the welding process are suspended for some time in the welding environment and through aspiration enter the internal parts of the lungs which can be dangerous to the health of the welder. The origin of gases as a respiratory pollutant in welding are the fuel gases, shielding gases and gases of the welding process [10]. Different gases, such as ozone (O3), nitrogen oxides (NOx) and carbon monoxide (CO), are produced and released during welding operations [11]. In many welding processes during arc formation, nitrogen oxides (NOx) form from the reaction of nitrogen and oxygen in the air [12]. Ozone is a strong oxidizing agent. It is caused by ultraviolet radiation on the surrounding arc of welding during the establishment of the electric arc [13]. Carbon dioxide is a greenhouse gas that plays a major role in global warming, climate change, and human activity [14]. Carbon monoxide could be a colouress, scentless and tasteless gas. Carbon monoxide is very dangerous because it can act as a deadly agent for the health of the person by reducing the oxygen-carrying capacity of the blood. However, at low concentrations, it causes headaches, dizziness, nausea, and physical weakness. Ozone stimulates the upper airways with coughing and chest compression [15]. Nitrogen dioxide (NO2) and nitrogen oxide (NO) are highly toxic gases, which greatly stimulate the eyes, nose, skin, and mucous membrane [16].

Welders are exposed to a range of metal fumes. Fumes are solid particles that are produced due to the condensation of gases and after sublimation from molten material. These particles are very tiny and therefore easily repairable [17]. Welding fumes have been introduced as “possibly carcinogenic to humans” (Class 2B). Different metals in the welding fume (manganese, cadmium, lead, and some nickel and cobalt oxides) are classified by IARC and the European Union as “carcinogenic agents” [18].

Studies have shown that at least 13 dangerous and toxic elements are released in the welding process [19]. Manganese (Mn) caused the resistance of the welding base metal and prevents cracking and subsequent welding defects. Mehrifar et al. conducted a study in a steel company in Iran. They reported that the exposure of welders to Mn is exceed the permissible limit and the frequency of migraine headache symptoms is also higher among the welders in comparison with the control group [20]. Exposure to manganese-containing fumes in the long-term results in a neurological disorder called manganism, a neurodegenerative disorder characterized by the abnormality of the central nervous system and neuropsychiatric disorders [21]. Manganese-containing fumes cause heterogeneities in the magnetic field and increase the rotation of brain protons, which results in shortening the brain resting cycle [22].

Chrome is one of the most toxic heavy metals and is widely used in many industries. Chrome may enter the body through direct breathing or direct contact with the skin (mainly in Cr (VI) form).This exposure may lead to blood problems, biochemical defects, and acute and chronic lung cancers [23]. The findings indicate that the prevalence of mortality from brain cancer is high among workers exposed to chromium in Japan and welders who use chromium-nickel steel [24].

Nickel is often used in industrial areas, where nickel is used to produce stainless steel and other nickel alloys [25]. Nickel is known as an acute toxic substance by many government agencies and international organizations, and is classified as a human carcinogen (Group 2B) by the International Agency for Research on Cancer (IARC) and the World Health Organization (WHO) [26]. Nickel can damage various organisms, and its toxicity significantly depends on its type, physical form, level of concentration and route of exposure [27]. Lippmann et al. in a study on poisoning, mortality and information from the air pollution database, found that daily mortality rates in 60 US cities were significantly related to average levels of nickel and vanadium [28].

Due to the significant expansion of welding activity and the increasing number of welders who work in industries and are exposed to metallic fumes and hazardous pollutants, the Semi-quantitative Risk Assessment (SQRCA) method can help identify pollutants and determine the level of exposure risk. The principles of risk assessment include risk identification, exposure assessment and risk characteristics [29]. No studies have been done regarding the determination and evaluation of the level of exposure risk of welders to metal fumes and types of gases caused by common welding processes in the steel industry. Hence, the purpose of this study is to assess the exposure concentration and determine the level of exposure risk of welders to metal fumes and gas pollutants in the steel industry.

2 Methods

2.1 Study design

This cross-sectional study was carried out at a steel industry in Iran. After selecting the industry and before the start of the research, the purpose of the study and the sampling method of fumes and gases for welders were fully described, and the study was approved by the university’s research committee. We used the census method and selected 55 male welders. The workers had to perform manual welding operations through the welding of metal parts and sheets. The types of welding included Shielded Metal Arc Welding (SMAW), Gas Tungsten Arc Welding (GTAW), Gas Metal Arc Welding with Inert Gas Welding (MIG) and Gas Metal Arc Welding with Active Gas Arc Welding (MAG).

2.2 Sampling and analysis

After the identification of pollutant stations, a sampling of gases and welding fumes was carried out. The O3 gas sampling was carried out by a Fiberglass Filters (diameter 37 mm) with a flow rate of 0.2 liters per minute using a personal sampling pump manufacturing (SKC, USA) and was based on the OSHA-214 method. For the analysis of samples of ozone, a UV-VIS spectrophotometer was used. NIOSH-6014 method and UV-VIS spectrophotometer were used for NO2 sampling and analysis. To sample CO and CO2, direct reading instruments CO 1372 meters and NDIR CO2 1370 (Tes, Italy) were used. Air samples from the breathing zone of the welders (a region between 15 to 23 cm from the front of individuals’ shoulders in accordance with OSHA instructions) were taken using a mixed cellulose ester (MCE) filter. Air sampling for collecting the welding fumes was done in accordance with the National Institute for Occupational and Safety (NIOSH) method 7300 [19] with a personal sampling pump (224-PCMTX8; SKC, USA) and MCE filter (25 mm, 0.8μm; SKC, USA), and a sampling pump calibrated with the digital calibrator (Defender-510, Canada).

2.3 Risk analysis

To estimate the level of exposure to contaminants, the Semi-Quantitative Risk Assessment of Chemicals (SQRCA) developed by the Department of Health and Safety of Malaysia [30] was used. Given the variety and widespread exposure to gases and metal fumes released in the welding operation, a health risk assessment was essential. After identification of the welding stations, the hazard rate, exposure rate and the risk level of each welding process and their pollutants were determined.

2.4 Hazard rate determination

According to Malaysian Department of Occupational Safety and Health, the degree of contamination risk can be assessed by considering the effects of acute toxicity of chemicals through lethal doses (LD50 = Dose Lethal50) and lethal concentration (LC50 = Concentration Lethal50) obtained by the Department’s recommended methodology. The next step was to determine the degree of exposure to identified substances (Table 1).

Table 1
Degree of risk acute toxicity

Risk factor LD50 absorbed orally in rats (mg/kg) LD50 absorbed through the skin in rabbits or rats (mg/kg) LC50 absorbed through the respiratory system in rats (mg/lit) for four hours for gas and steam LC50 absorbed through the respiratory system in rats (mg/lit) for airborne particles

2 2000< 2000< 20< 5<

3 200 < LD50 < 2000 400 < LD50 < 2000 2 < LC50 < 20 1 < LC50 < 5

4 25 < LD50 < 200 50 < LD50 < 400 0.5 < LC50 < 2 0.25 < LC50 < 1

5 <0.25 <50 <0.5 <0.25

Risk factor	LD50 absorbed orally in rats (mg/kg)	LD50 absorbed through the skin in rabbits or rats (mg/kg)	LC50 absorbed through the respiratory system in rats (mg/lit) for four hours for gas and steam	LC50 absorbed through the respiratory system in rats (mg/lit) for airborne particles
2	2000<	2000<	20<	5<
3	200 < LD50 < 2000	400 < LD50 < 2000	2 < LC50 < 20	1 < LC50 < 5
4	25 < LD50 < 200	50 < LD50 < 400	0.5 < LC50 < 2	0.25 < LC50 < 1
5	<0.25	<50	<0.5	<0.25

2.5 Exposure rate determination

According to the guidance provided by the Malaysian Department of Occupational Safety and Health, the degree of exposure can be obtained via the actual exposure level (pollutant measurement results). To calculate exposure rate (ER), two basic factors are used: weekly exposure (E) and Occupational Exposure Limit (OEL). Weekly exposure is estimated using the following equation. $E = \frac{F \times D \times M}{W}$ where E = Weekly exposure (ppm or mg/m³), F = Exposure repetition per week (number per week), M = Exposure (ppm or mg/m³), W = Average working hours per week (40 hours), and D = Average duration of exposure (hours).

The exposure value (E) obtained from the above equation was compared with the Occupational Exposure Limit (OEL), then the exposure coefficient (ER) was determined from Table 2.

Table 2
Exposure rate

Exposure rate (ER) E/PEL

1 <0.1

2 0.1–0.5

3 0.5–1

4 1–2

5 2≤

Exposure rate (ER)	E/PEL
1	<0.1
2	0.1–0.5
3	0.5–1
4	1–2
5	2≤

2.6 Risk score determination

In this step, the risk score was calculated according to the chemical hazard rating (HR) and exposure degree (ER) using the following equation: $Risk Score = \sqrt{HR \times ER}$

2.7 Rating risk

After determining the risk scores for each of the materials examined, the rating risk was obtained using the risk rating table (Table 3) for rating each of the materials in order to design control measures. Finally, the exposure level was determined by considering five levels of abandonment (N): low (L), moderate (M), high (H) and very high (VH).

Table 3
Risk rating

Risk score Ranking Risk rate Necessary actions

0–1.7 Negligible N End of evaluation, reassessment every 5 years

1.7–2.8 Low L Non-continuous air sampling, reassessment every 5 years

2.8–3.5 Medium M Continuous air sampling, reassessment every 4 years

3.5–4.5 High H Completion of engineering controls, air sampling, personal protective equipment

4.5–5 Very high VH Completion of engineering controls, air sampling, personal protective equipment, setting emergency procedures

Risk score	Ranking	Risk rate	Necessary actions
0–1.7	Negligible	N	End of evaluation, reassessment every 5 years
1.7–2.8	Low	L	Non-continuous air sampling, reassessment every 5 years
2.8–3.5	Medium	M	Continuous air sampling, reassessment every 4 years
3.5–4.5	High	H	Completion of engineering controls, air sampling, personal protective equipment
4.5–5	Very high	VH	Completion of engineering controls, air sampling, personal protective equipment, setting emergency procedures

Finally, measures were adopted to control and reduce the risk of exposure of welders to pollutant emissions to acceptable levels through the removal of hazardous materials from the workplace, replacing chemicals with low-risk chemicals, managing practices such as workflow, limiting exposure, and using clothes and personal protective equipment.

2.8 Data analysis

The collected data were analyzed by SPSS software version 21 (SPSS Inc., Chicago, IL, USA).

3 Results

The results of exposure of welders to gases according to the type of welding process are presented in Table 4. Welders’ ranges of measured mean concentration to carbon monoxide (CO), nitrogen monoxide (NO), nitrogen dioxide (NO2) and ozone (O3) were 35–52.37, 15.23–42.65, 2.88–6.49, and 0.18–1.97 ppm, respectively. The average range of exposure concentration of welders to manganese, chromium and nickel fumes was 1.16–3.59, 1.73–5.18, 0.66–1.97 mg/m³, respectively.

Table 4
Mean and standard deviation of the concentration of welders’ exposure to gas contaminants in welding processes

Type of fume SMAW MAG MIG GTAW Total

CO 43.50±11.19 41.33±9.74 52.37±14.16 35±4.462 43.05±9.88

NO 18.15±5.88 35.50±11.49 42.65±15.87 15.23±4.19 27.88±8.30

NO2 3.63±1.02 4.22±0.94 6.49±1.38 2.88±1.65 4.30±1.24

O3 0.38±0.09 0.43±0.12 0.65±0.21 0.18±0.05 0.41±0.11

Type of fume	SMAW	MAG	MIG	GTAW	Total
CO	43.50±11.19	41.33±9.74	52.37±14.16	35±4.462	43.05±9.88
NO	18.15±5.88	35.50±11.49	42.65±15.87	15.23±4.19	27.88±8.30
NO2	3.63±1.02	4.22±0.94	6.49±1.38	2.88±1.65	4.30±1.24
O3	0.38±0.09	0.43±0.12	0.65±0.21	0.18±0.05	0.41±0.11

The results showed significant increases in mean exposure to gases CO, NO2 and O3 compared to the threshold limit value - time weighted average (TLV-TWA) recommended by the ACGIH, which showed a P-value <0.05. The average NO concentration was 27.88±8.30 ppm, which was lower than TLVs-TWA (ACGIH). The maximum and minimum mean concentrations of exposure to all gases studied were observed in MIG and GTAW, respectively. Other findings also showed that the average concentrations of exposure to Mn, Cr, and Ni metals were significantly higher than TLVs-TWA (ACGIH) (P-value <0.05). Maximum and minimum concentrations of exposure to all the studied metals were observed in SMAW and GTAW, respectively (Table 5).

Table 5

Mean and standard deviation of the concentration of welders’ exposure to metal fumes in welding processes

Average concentration of exposure (mg/m³)
Type of metal	SMAW	MAG	MIG	GTAW	Total
Chromium	5.18±1.51	3.80±1.41	2.06±0.77	1.73±0.75	3.19±1.37
Nickel	1.97±0.36	1.45±0.23	0.87±0.36	0.66±0.20	1.24±0.61
Manganese	3.49±0.83	2.41±0.61	2.04±0.81	1.16±0.48	2.30±0.76

In Tables 6 and 7, hazard rate (HR), exposure rate (ER), quantitative risk score and level of exposure risk to metal fumes and gas pollutants in various welding processes are presented.

Table 6

Hazard rate, exposure rate and risk rating of exposure to gaseous contaminants in the studied welding processes

Type of welding	Gas contaminants	HR	ER	RR	Assessment
SMAW	CO	4	4	4	H
	NO	1	1	1	N
	NO2	4	5	4.45	VH
	O3	5	5	5	VH
GMAW-MIG	CO	4	4	4	H
	NO	1	3	1.73	L
	NO2	4	5	4.45	VH
	O3	5	5	5	VH
GMAW –MAG	CO	4	4	4	H
	NO	1	1	1	N
	NO2	4	5	4.47	VH
	O3	5	5	5	VH
GTAW	CO	4	4	4	H
	NO	1	2	1.41	N
	NO2	4	5	4.47	VH
	O3	5	5	5	VH

N: Negligible H: High VH: Very high.

Table 7

Hazard rate, exposure rate and risk rating of exposure to metal fumes in the studied welding processes

Type of welding	Metal fumes	HR	ER	RR	Assessment
SMAW	Cr	5	4	4.47	VH
	Ni	3	3	3	M
	Mn	2	5	3.16	H
GMAW-MIG	Cr	5	5	5	VH
	Ni	3	1	1.73	L
	Mn	2	5	3.16	H
GMAW –MAG	Cr	5	3	3.87	H
	Ni	3	1	1.73	L
	Mn	2	3	2.44	M
GTAW	Cr	5	1	2.23	M
	Ni	3	1	1.73	L
	Mn	2	2	2	L

L: Low, H: High, VH: Very High, M: Middle.

As shown in Table 6, among the gases, the highest risk rate is related to ozone and nitrogen dioxide in each of the four types of welding with a very high (VH) hazard rate. Also, the lowest level of exposure risk in all types of welding is related to nitrogen monoxide with a negligible (N) hazard rate. Carbon monoxide had a hazard rate of high (H) in all types of welding.

The results of Table 7 show that among metals, the highest hazard rate is related to chromium and manganese in all four types of welding with a hazard rate of high (H) and very high (VH). The lowest exposure risk rate in all types of welding is related to nickel with low (L) and medium (M) hazard rate. SMAW and GTAW welding had the highest and lowest risk rate among the welding processes studied, respectively.

4 Discussion

With the advent of new types of welding processes and their applications, the number of welders exposed to fumes and gases generated during welding is also increasing and, consequently, the health risk of exposure to these pollutants also increases [31]. Gases and fumes from welding operations can enter the respiratory system and have irrecoverable effects on the health and wellness of the welders. In the present study, welders were mainly exposed to four gaseous pollutants during welding: NO, NO2, CO and O3. The exposure rate of welders to the average total gas showed that MIG welders are exposed to higher levels of pollutant gases than other types of welders (Table 2). This may be due to the time of the welder’s activity at the welding station, the use of shielding gas, the absence of a suitable local ventilation system at the welding station and the location of the relevant welding site. This finding is consistent with the study by Popović et al., who found that concentration of carbon monoxide and carbon dioxide in MIG welding is higher than MMAW and SMAW welding [8].

The findings of this study showed that the concentration of CO, NO2 and O3 gases was 2, 22 and 8 times the TLV-TWA (ACGIH), respectively. This is probably due to the duration of continuous welding, the high electrical voltage of the welding operation, the indoor area of the welding place, and the lack of localized ventilation in the welding place. Karimi Zeverdegani et al. reported that in the steel industry the concentrations of O3, Co and NO2 gases to which welders were exposed were higher than TLVs-TWA (ACGIH) [32]. Vander et al. conducted a study on MIG and TIG welders in The Netherlands. The results of their study showed that O3 was higher than TLVs-TWA (ACGIH) among NO, NO2 and O3 gases [33]. Results of our study showed that the concentration of NO was lower than the allowed values, which is consistent with the results of Golbabaei et al. [29].

A comparison of the exposure to metallic fumes in the studied welding indicated that workers in SMAW welding have higher exposure to metal fumes compared to other welding methods (P-value >0.05). The higher amount of fume in this type of welding may be attributed to the frequency and duration of welding throughout the day and week.

This finding is consistent with the finding by Hasani et al. who found that SMAW welders were more exposed to metal fumes compared to MMAW welders [34]. On the other hand, the study by Michael et al. found that burning one gram of electrode coatings between GMAW, SMAW and, FCAW welding processes, SMAW produces the largest amount of metal fusion. A recent study at a machine-building factory confirmed that exposure to hexavalent chromium and total fume in SMAW welding is higher than in GMAW welding [35].

In our study, all metals in SMAW welding were at their highest concentration levels. These findings are consistent with previous studies [10]. Pacheo et al. conducted a study on a variety of welding processes and found that the amount of iron, manganese, cadmium and chromium fumes generated during the welding process SMAW was higher compared to the various types of welding [36]. This result is consistent with our findings. Perhaps the reason for the high amounts of metals in this type of welding is the formation of fume and welding gases by the factors such as current and voltage used period and nature.

In the semi-quantitative risk assessment (SQRCA), the results showed that the highest exposure risk to fumes in welding types belonged to SMAW welding operator and the lowest risk was related to GTAW welding. These risk assessment results are consistent with the results of the sampling and actual measurement of pollutants in the workplace. On the other hand, regarding the nature of the metallic pollutants, the highest and lowest risk was related to chromium and nickel, respectively. The results of the risk assessment of gas pollutants showed that the highest risk is related to SMAW welding and NO2 and O3 gases with a very high risk rate. This finding is consistent with the results by Mehrifar et al., who studied the welders of a steel company in Iran. They reported that ozone and nitrogen oxide gases released in welding operations have a very high risk rate [37]. This study has some limitations: (1) Small sample size and lack of cooperation of welder, and (2) they did not consider other environmental parameters such electric current intensity, voltage, or type of electrode.

The results of the semi-quantitative risk assessment showed that the risks in the workplace can be prioritized to provide the necessary control measures. In activities with high concentrations of pollutants, a semi-quantitative risk assessment should be used, if possible, in addition to the air sampling and biological monitoring. Also, reducing exposure levels by installing appropriate local ventilation systems, modifying work procedures, and using respiratory protection equipment should be considered.

5 Conclusion

The results of work environment monitoring showed that welders in most welding processes, but especially SMAW, are at a high level exposure to gases and fumes generated during the welding process. The results also showed that some gases, especially CO, NO2 O3, and fume of chromium and manganese in all types of welding, had a high (H) and very high (VH) risk rate. Therefore, periodic monitoring of the air pollutants of the welding environment and risk assessment of the SMAW welders must be carried out on a regular basis. Occupational health welders are required to apply preventive measures such as installing periodic screening health examination, local exhaust ventilation systems, and providing respiratory protection (RP) devices for welders.

Conflict of interest

None to report.

Funding

This study was financially supported by a master’s thesis.

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Chemical pollutants in the respiratory zone of welders: Determination of concentrations and hazard analysis

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1 Introduction

2 Methods

2.1 Study design

2.2 Sampling and analysis

2.3 Risk analysis

2.4 Hazard rate determination

Table 2 Exposure rate Exposure rate (ER) E/PEL 1 <0.1 2 0.1–0.5 3 0.5–1 4 1–2 5 2≤

2.7 Rating risk

3 Results

5 Conclusion

Conflict of interest

Funding

References

Table 2
Exposure rate

Exposure rate (ER) E/PEL

1 <0.1

2 0.1–0.5

3 0.5–1

4 1–2

5 2≤