Author: Peter B. Harnett, MS, MPH, CIH
Why conduct personal air sampling?
The OSHA standard 29 CFR 1910.1000 “Air contaminants,” effectively requires air sampling to determine compliance with materials for which OSHA has standards. OSHA does have standards for particulates, crystalline silica, nitrogen dioxide, and several volatile organic compounds (VOCs) some of which are known to be present on natural gas and oil hydrofracturing sites.
Personal air sampling needs to be performed for crystalline silica (NIOSH evidence already indicates common exceedances of OSHA standards for crystalline silica at hydrofracturing sites.) It is possible that other OSHA standards for particular compounds or particulates may also be exceeded. It is important to perform personal air sampling to meet OSHA requirements and more importantly to determine if there are problematic levels of air contaminants that employees are exposed to onsite.
Selection of appropriate respiratory protection is based on personal air sampling results. It is difficult for an employer to justify respiratory protection selection without personal air sampling results.
NIOSH is already involved in performing personal air sampling at hydrofracturing sites and has demonstrated exposure concerns for crystalline silica. Mr. Eric Esswein at NIOSH indicates that aside from crystalline silica, air sampling is indicated for diesel particulates, particulates, nitrogen oxides and VOCs. OSHA is likely to act on these data and make visits to hydrofracturing sites with the purpose of identifying health and safety issues on the sites. (Crystalline silica is already listed on OSHA’s National Emphasis program.) The employers’ best interests are served by developing an understanding of personal air contaminant exposures prior to OSHA visits.
Perimeter air sampling is useful for several reasons. The information can provide some realistic estimates of the site’s offsite contribution to air quality. The results of the perimeter air sampling data can be utilized in models to estimate air contaminant levels at offsite locations. Additionally, local residents are likely to be pleased that site operators took the time and resources to determine the air contaminants and concentrations that could move offsite and potentially affect residents.
An employer should initially perform area air samples to characterize the degree of exposure to contaminants for different site activities. With this information the employer can direct personal air sampling efforts to employees more likely to show elevated exposure to some onsite air contaminants.
Some likely personal air exposures exist for crystalline silica (Sand is used as a proppant.), nitrogen oxides (diesel pump exhaust), VOCs (wells and several onsite activities), particulates including PM2.5 fraction (diesel pump exhaust) and inhalable portions (diesel pump exhaust). There has been a great deal of recent press about the carcinogenicity of fine diesel engine exhaust largely resulting from the World Health Organization’s International Agency for Research on Cancer’s June 2012 conclusion that diesel engine exhaust is a human carcinogen.
For site perimeter monitoring use real-time instruments, e.g., TSI DustTrak with particle size cutoff limits to determine particulate levels and the HNU Photoionizer or equivalent for volatile organic compounds (VOCs). Choose multiple locations on the site perimeter for these measurements, because wind direction and speed change, distance from site activities… show intraday and interday variability. For planning purposes local meteorological data patterns should be useful for approximations of cardinal wind direction, wind speeds, etc. during particular time periods through the year.
The perimeter monitoring data should then be analyzed to determine likelihood of potential employee exposure issues based on area samples proximate to onsite activities and potential community exposure issues based on site perimeter work.
The selection of personal samples should be based on area air samples results. If elevated personal air concentrations of crystalline silica, particulates, nitrogen oxides and/or VOCs are found, it is important that employees wear appropriate respiratory protection to maintain exposures below applicable OSHA standards. Companies should also be exploring engineering controls and work practices to reduce employee exposure. VOC analysis should initially be performed to identify specific volatile organics present. In natural gas and oil exploration aromatic compounds including benzene, toluene, ethyl benzene and xylenes are likely to be present near the well. Additionally, these compounds each have published OSHA Permissible Exposure Limits (PELs). GC/MS analysis is recommended. Analysis of the initial personal results for VOCs will inform approaches to future VOC personal air sampling.
Perimeter air sampling with fixed sampling techniques will be used to provide more accurate and precise results than real-time measurements. For VOC analysis, GC/MS analysis should be performed to identify specific VOCs found at the site perimeter. (Elevated VOC levels will result in elevated ozone levels.) Perimeter particulate levels should initially be compared with National Ambient Air Quality Standards (NAAQS). Levels above the NAAQS may be expected downwind from onsite activities that produce dust.
The information gathered from site perimeter air sampling is a useful stepping off point for communications with local residents. Some of the residents will express concern about the site activities creating harmful air pollutants. By conducting the perimeter air sampling, it is a demonstration to the local residents that the site operators are concerned with local residents and the possibility that the movement of air contaminants offsite could pose an issue.