Sampling Technique

For personal sampling, the position of the sampling medium should allow the device to collect air from the employee’s breathing zone. This is defined by OSHA in the U.S. as a two-foot diameter sphere centered in the middle of the head. For welders, the filter medium should be placed inside the welding helmet because the helmet provides some protection and inaccurate results would be obtained otherwise. The pump, which is frequently worn on a belt, and the tubing should not impede the worker’s activities or pose a safety hazard.

In all cases, the employees’ support should be sought by explaining the reason for sampling and asking for their participation. Employees should also be instructed to notify the supervisor or person conducting the sampling if the equipment malfunctions or if they need to have it removed.During the shift, periodic checking of the battery charge and pump flowrate should be performed and documented to ensure sample validity and accurate volume calculation. This is especially important in very dusty operations where high filter loadings may occur and cause the pump flowrate to decrease. Some pumps are designed to compensate for this by automatically increasing the pump speed and, thus, the flowrate; however, periodic checks are still recommended. The person doing the sampling should also note the temperature and barometric pressure so that adjustments to the volume of air collected can be made.

Through work observation, a job description should be developed that includes information about work practices and other factors that potentially influence exposures. This can be used to explain sample results and to aid in decisions on exposure control should the need arise. This information may include production rates, time spent on breaks, the use of ventilation, work practices, and proximity to the source of exposure. In addition to recording descriptive information and documenting pump checks, the collection sheet can serve as a log for ambient conditions relevant to sample collection, pump and filter media identification numbers (including sample blanks), and sample duration. Any use of respiratory protection also should be documented.