ALS can help refineries monitor the fenceline of their facilities for concentrations of benzene and other volatile organic compounds (VOCs).
ALS provides testing solutions for refineries to monitor the fenceline of their facilities for concentrations of benzene and other volatile organic compounds (VOCs).
Although benzene is the primary target compound for most regulations, the sampling and analysis methodology can also be used to determine other VOCs, including 1,3-butadiene, toluene, ethylbenzene, xylenes, and other hazardous air pollutants.
EPA Method 325, Volatile Organic Compounds from Fugitive and Area Sources, was created for monitoring the fencelines of refineries for benzene and includes two sub-part methods:
- EPA Method 325A: Sampler Deployment and VOC Sample Collection.
- EPA Method 325B: Sampler Preparation and Analysis.
These complementary US EPA methods outline the design, deployment, preparation, and analysis of a series of passive sampling devices suspended around the refinery property line.
In an effort to adequately provide spatial coverage to determine representative pollutant concentrations, the US EPA has specified 12 to 24 diffusive samplers must be deployed on a bi-weekly basis to monitor benzene concentrations around the fenceline of every refinery property. The number of samplers is based on the size of the refinery (<750 acres, 750 to 1,500 acres, and >1,500 acres). The concentration of benzene on the samplers must be monitored on an annual rolling average basis in order to determine if there are significant excess emissions of fugitive sources that need to be addressed.
How Does Passive Sampling Work?
On the sampling end of the tube, the cap is removed and replaced by a diffusion cap. The diffusion cap mitigates against wind variables and allows the space in the tube to reach the same concentration as the ambient concentration.
For compliance with EPA Method 325, the tube hangs sampling end down and the shelter protects it from debris and rain. Over the course of the two-week sampling period, the target compounds migrate to the surface of the sorbent and are captured on the surface.
Passive sampling sorbent tubes are analyzed using a thermal desorption device. This works by heating the sample tube and releasing the compounds into a flow of inert gas. Once sample is focused, it is heated again and rapidly injected into the GC column in a narrow band of vapor.
Sample media & deployment
Sorbent tubes are extremely versatile and can be deployed for weeks at a time. The tubes are deployed for 14 days at location points outlined per EPA Method 325A (either equal linear distance between samplers or equal degrees of separation around the geometric center of a facility). After sampling is complete, the tubes are capped and sent to the laboratory for analysis.