Prior to sampling for welding fumes and gases, an industrial hygienist must perform pre-inspection activities. The industrial hygienist’s job is to monitor the chemicals contained in the fumes and gases. Industrial hygiene sampling during welding activities depends on three main factors including the type of welding being performed, the ingredients in the welding electrode, and the type of base metal being welded. The typical amount of welding time and the types of controls used to reduce exposure must also be taken into consideration before sampling. The accuracy of the sampling results greatly increase if an industrial hygienist accurately prepares equipment, media and supplies prior to sampling.
This discussion focuses on factors that an industrial hygienist must consider in order to develop a sampling plan during the pre-inspection phase, and outlines how those factors affect the sampling overall.
Type of Welding
The three most common types of welding that Colden consultants encounter are shielded metal arc welding (stick welding), metal inert gas (MIG) or gas metal arc welding), and tungsten inert gas (TIG) welding. Depending on the type of welding, the following factors may vary in importance during the on-site inspection process:
- Total number of sampling cassettes to be used during sampling. Sample cassettes can become over loaded during stick and metal inert gas (MIG) welding.
- Welders tend to avoid using local exhaust ventilation (LEV) during TIG welding.
- The shielding gas may vary depending on the type of welding.
Other types of welding to be aware of include flux-cored welding, arc welding and plasma arc welding.
Ingredients in Electrode and Base Metal
The industrial hygienist should review the safety data sheet (SDS) to determine the constituents of the welding electrode and base metal. Depending upon the components listed on the SDS, the industrial hygienist will be able to review and make decisions on the following:
- Type of sampling media.
- Number of sampling cassettes needed to sample the prioritized contaminants during welding.
- Number of sampling pumps.
- Exposure limits of the contaminants to be sampled. Including identifying which contaminants have short term exposure limits (STELs).
- Are shielding gases used and is additional sampling required as a result. For example, carbon dioxide is a typical shielding gas, and can produce carbon monoxide in areas with poor ventilation.
Time and Severity of Exposure
The typical duration of an employee’s shift and the length of welding exposure helps to determine the amount of sampling time required. Typically, sampling is performed according to 8-hour work shifts when comparing results to Occupational Safety and Health Administration (OSHA) exposure limits. Many employees do not perform welding for the entire duration of their work shifts, so it is important to know the length of time welders actually perform welding. For contaminants with 8-hour time weighted average permissible exposure limits a full-shift sample would be advisable to consider along with a task based sample.
Prior to on-site sampling activities, a preliminary review of preventative measures to reduce exposures should be completed as well. A more thorough evaluation of these controls will take place on-site. The following questions are relevant:
- What type of local exhaust ventilation (LEV) is being used? Will an air velocity meter be needed to evaluate its performance?
- Does the industrial hygienist need smoke tubes to test the direction of the airflow?
- Does the employee wear a welding helmet? What type of welding helmet? How will the welding helmet affect the positioning of the sampling cassette?
- Does the employee use a respirator, and if so what type? How will the respirator affect the positioning of the sampling cassette?
- Is the welding performed in any type of enclosure? If so, are there any byproducts of the materials and gases which may create additional hazards to the employees?
During on-site welding fume and gas sampling activities, there are several avoidable mistakes that can occur. Common errors include neglecting to:
- Use a separate cassette to account for contaminants which can not be analyzed on the same cassette. These metals include, but are not limited to, hexavalent chromium and silver.
- Test the capture velocity of LEV during sampling to ensure that the system works properly.
There is much debate about the position of the sampling cassette. Certain situations and company policies require sampling inside the helmet and other require sampling outside of the helmet. Whichever approach is taken should be aptly noted.
It should be noted the pre-inspection activities outlined above are not necessarily the only factors to consider in preparation for an industrial hygiene sampling study but rather a good start.