Post Asbestos Abatement Clearance and Air Sampling
The EPA/AHERA regulatory clearance level for asbestos abatement projects in K-12 schools depends on the analysis type. For phase contrast microscopy (PCM) analysis, the level is 0.01 f/cc or lower, based on each result of at least five samples per abatement area. For transmission electron microscopy (TEM) analysis, the level is 70 s/mm2 or lower, based on the average of at least five samples per abatement area.
The sample air volumes normally required to measure these levels are at least 3,850 liters for each sample analyzed by PCM and at least 1,200 liters for each sample analyzed by TEM. These clearance levels are mandatory for school abatement projects and EPD highly recommends their use for non-school projects.
EPD often sees clearance and personal air sampling records that cause the results to be questioned. Examples of this include when sampling records indicate that:
- All sampling periods started and stopped on the hour
- All sampling periods started and stopped at the same time
- All sample flow rates were even numbers and were the same from pump to pump and from day to day
While all these cases are possible, it is not what usually happens on a project. The flow rates of pumps should be measured with devices that are traceable to primary calibration devices, such as bubble-burettes or electronic calibration devices. Rounding off of data should be avoided beyond the second significant digit (i.e., 3.00 L/min vs. 2.92 L/min). Rounding can create a multiplier effect resulting in variations as much as +/- 23% in the final value.
Accurate and detailed records are essential and should be maintained for sample times, flow rates, calibration checks, and all other pertinent facts. Consider these issues and discuss them with the appropriate persons for your projects. It could save you from regulatory or liability issues being that exposure assessment issues (air sampling and analysis) are the items most frequently cited by OSHA under the 1926.1101 asbestos standard.