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Fenceline Monitoring

Fenceline monitoring is the use of monitoring technology to measure the ambient air concentration at the property line or perimeter of a manufacturing site (e.g., petroleum refinery, chemical plant) for a specific chemical. A work practice standard for fenceline monitoring was promoted by the United States Environmental Protection Agency ("US EPA") as an appropriate method to provide open and transparent evaluation of a site’s emissions monitoring and control methods on an on-going basis.


To achieve that goal, US EPA developed this work practice and published it in December 2015. This work practice specified the monitoring technology to be used, an implementation approach, and a benzene fenceline concentration action level above which owners or operators would be required to implement corrective action to reduce their fenceline concentration to below this action level. The details of the fenceline monitoring work practice is prescribed in EPA Test Methods 325A and 325B.


This is the work practice that ExxonMobil uses for our fenceline monitoring programs. In fact, there are over 150 different refineries and chemical plants in US and Canada utilizing this technology and work practice for fenceline monitoring.

What is fenceline monitoring?


Fenceline (or perimeter) monitoring is the use of monitoring technology to measure the ambient air concentration of a specific chemical at the property line of a manufacturing site (e.g., petroleum refinery, chemical plant).


How it works


The air samples are collected by tubes, which are filled with an absorbent and switched out every two weeks. Once removed, the tubes are sampled at an independent accredited laboratory.


Did you know?


The science of absorption is one we are familiar with in our daily lives. Examples are using paper towels to absorb liquids from the counter or baby diapers. The difference in fenceline monitoring is that after we absorb the chemicals in our tubes, they are later desorbed (i.e., absorbed chemicals removed from the absorbent) in the lab so that how much we collected can be measured.