Air Alliance Houston and Milby High School conduct toxics monitoring

Recently, Air Alliance Houston joined forces with students from Milby High School to conduct air monitoring in east Houston. This effort is the latest project in a semester long partnership we have had with Jeff Stear, an Engineering Teacher (Lead) in the IPAA/PESA Petroleum Academy at Milby High School. All semester, Milby students in Mr. Stear’s class have learned about the refining industry and its impact on their health.


In the Environmental Protection Agency’s new refinery air toxics rule, the agency has proposed to require that refineries begin measuring the amount of benzene that leaves their facilities. This so-called “fenceline” monitoring would be performed using a type of sampler known as a passive sorbent tube. The monitor is called “passive” because it simply sits and collects air that moves over it. This is in contrast to “active” monitoring technologies like UV-DOAS, which can measure for hundreds of compounds in real time.


Monitoring for benzene is important. As the Milby High School students learned, benzene is a known human carcinogen that has significant public health impacts here in Houston. If students are exposed to benzene where they live or go to school, then their health is at risk. These sorbent tubes are very sensitive as passive technologies go, but they cannot compete with active technologies, which we would prefer be used. We are concerned that passive samplers are simply not adequate to measure the health risk benzene presents. We decided to test the monitors by placing some of our own around Milby High School.


We placed 3 samplers in total. One in Manchester on the fenceline of the Valero refinery, one at Milby High School itself, and one at the Mission Milby Community Center. The samplers stayed in place for two weeks, after which time we sent them to a lab for analysis.


Benzene is present in the ambient air around oil refineries. The EPA states that that an ambient air level of 0.13 µg/m3 leads to a 1:1,000,000 increased cancer risk for a lifetime of exposure. In its new refinery air toxics rule, the EPA has proposed a two-week limit of 9 µg/m3 , meaning that corrective action would be required if a sample exceeded that limit. The samples we took came back as follows:

Valero Fenceline: 1.2 µg/m3

Mission Milby: 1.1 µg/m3

Milby High School: 0.82 µg/m3

So all three samples were well above the level that would lead to the 1:1,000,000 increased cancer risk after a lifetime of exposure, but well below the action level proposed in EPA’s new refinery rule. (We also sampled for three other carcinogens: toluene, xylene, and ethylene. These compounds were also found in the range of 0-3  µg/m3. Our analysis focuses on benzene because EPA has proposed a fenceline standard for benzene only.)

There are many limitations to this method of sampling. Were there any large spikes of benzene during the two weeks we sampled? We have no way of knowing, because the sampling methodology averages the concentration of benzene in the air over the entire two-week period. Suppose a dangerous spike of benzene had occurred, a passive sampler wouldn’t tell anyone anything about that as it was happening. Only active technologies can identify short term changes in air pollution in real time. We don’t think it is very useful to tell residents two weeks after the fact that they’ve been exposed to unhealthy levels of air pollution.

We are going to continue testing these sorbent tube samplers. The refinery air toxics rule is the first time EPA has ever proposed fenceline monitoring in any rule. We are still asking the EPA to require active fecneline monitoring with a system such as UV-DOAS, but for now, these tubes are the best we have. We will continue to explore their use in order to decide for ourselves whether they can provide adequate protection for fenceline communities.


Thank you to Jeff Stear and the students of Milby High School who joined us in this project!