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Air Monitoring During the U.S. Steel Clairton Coke Works Fire & Repair Period Explored & Explained

Updated: Dec 20, 2022

Typical raw coke oven gas is largely hydrogen (52 percent-59 percent) and methane (26 percent-33 percent) but among other minor constituents includes 0 percent-1 percent benzene and 0.4 percent-1.2 percent hydrogen sulfide (H2S)-all percent by volume.

The raw coke gas stripped of much of the sulfur content is normally burned as fuel for heating in the Clairton batteries, as well as the other U.S. Steel Mon Valley plants. Upon combustion, the remaining hydrogen sulfide component of raw coke gas largely converts to sulfur dioxide (SO2).

The benzene constituent normally also passes through pollution treatment. Benzene will diminish in a combustion process as well.

Raw coke oven gas containing H2S, benzene and particulates can also leak directly from the battery ovens during coking operations (baking of the coal). Before or after the facility fire, oven leakage of raw coke gas is a pollution issue demanding strong surveillance and remediation.

As the days and weeks passed, air pollution control improvements and air quality monitoring included the following:

Natural gas which contains fewer pollutants than coke oven gas was blended into the raw coke gas/fuel stream.

Flaring (burning) of the untreated coke gas took place at the U.S. Steel Irvin Works flares. All the plants— Clairton, Irvin, and Edgar Thomson—have connected piping to deliver typically stripped coke oven gas/fuel from the coking process. Flaring burned off many of the volatile organic compounds (VOCs) including some toxics and diluted the combusted coke oven gas emissions with ambient air as the hot emissions plume expanded into the atmosphere.

Coking times were extended, which decreased the quantity of raw coke gas created per hour.

Two new special purpose air quality monitors measuring SO2, (in Clairton at the Clairton Educational Center and in West Mifflin at the New Emerson Elementary School) were added to existing air quality monitors located at Lincoln, Glassport, North Braddock, Clairton and Liberty. The new Clairton SO2 monitor is a bit upwind of the Clairton Plant if the wind is blowing from a typical southwest direction.

According to the Allegheny County Health Department (ACHD), the West Mifflin air quality monitor, sited approximately north-north east of the Irvin Works may record emissions flow along the Mon River from the Irvin Works. These new monitors are noted by ACHD to be temporary.

Monitor Locations

Check out the image below to orient yourself: The Clairton Coke facility is roughly across the river from the Lincoln monitor. Irving plant is across the river from Glassport. The North Braddock monitor is a short distance from Edgar Thomson which would be slightly above this graphic frame and it measures SO2 and particulates.

The Liberty air quality monitor is typically in a downwind direction of the Clairton facility. There is a recent privately operated toxics monitor at the ACHD Glassport monitor site.

Exceedances of Ambient Standards During the Fire and Repair Period

By way of background: SO2 and fine particulates are criteria pollutants known to have significant adverse health effects. Criteria pollutants have health-based concentration limits.

The 24–hour average PM2.5 limit and the one-hour sulfur dioxide limit are the air quality standards that have been reported as above or below the standard in Allegheny County Alerts, throughout the repair period.

A summary of ACHD activities and public information provided during the repair period can be found here. Following are some key takeaways:

  1. The 1-hour SO2 standard is 0.075 parts per million (ppm) or 75 parts per billion (ppb).

  2. Sulfur dioxide 1-hour exceedances of the federal standard occurred on six days at the Liberty Monitor from the date of the fire through April 3. Some days had more than one SO2 1-hour exceedance. At the Liberty monitor there was a total of eight one-hour SO2 exceedances.

  3. Sulfur dioxide 1-hour exceedances were noted on two days at the North Braddock Monitor during that time period.

  4. The 24–hour average fine particulate standard is 35 micrograms per cubic meter. There were three exceedances between the date of the fire and April 3 at the Liberty monitor.

  5. There were no SO2 or PM2.5 exceedances at the other Mon Valley monitors during the fire and repair period.

  6. Note that all data is tentative until quality is assured.

Another perspective on SO2 emissions is the direct facility limits, not at the ambient air quality monitor, but in the air permit issued by the Allegheny County Health Department, (ACHD). There were calculated exceedances of the H2S permit limits of 35 grains/100dscf (grains per hundred dry standard cubic feet) for Clairton Coke Works, Irvin, and Edgar Thomson.

For example the H 2S average daily grain loading four days before the fire was 6.08 grains/dscf and 36 days after the fire was 161.97 grains/dscf at batteries 19, 20, B and C (data noted from ACHD Enforcement Order 190202).

But What About Other Coke Gas Pollutants Like Benzene, Hydrogen Sulfide and Other Toxics?

There has been little mention of two other types of air pollution of concern to most people in the Mon Valley: benzene and hydrogen sulfide (H2S). While neither is a criteria pollutant with a federal health–based standard, benzene and H2S are products of the coking process.

They matter in different ways. Benzene is one of the most toxic constituents in coke gas and a known human carcinogen. Hydrogen sulfide has a window–slamming rotten egg odor noticeable at low concentrations—ruining many restful nights and morning walks.

Since there are no federal ambient air quality standards for benzene, many states and other agencies have done or collected research to suggest health risk concentration limits for benzene and other toxics. The World Health Organization has noted that “no safe level of exposure can be recommended (for benzene).”

More About Benzene

Chart 1 is the latest ACHD benzene chart from the Liberty Monitor where a 24-hours charcoal tube sample is taken every 3 days.1

Chart 1 (below) is the latest ACHD benzene chart from the Liberty Monitor, where a 24-hours charcoal tube sample is taken every three days:

(Credit: ACHD)

The bulk of charcoal tube sampling taken through the repair period in 2019 is not yet available but several days of data and a spike on 12/28 just after the fire can be observed.

Note that the Liberty benzene data before the fire has many spikes. One data point is over 10 ppb which would be above the ATSDR suggested (one– 14 day) limit.

According to the Allegheny County Air Quality Annual Report for 2017, 1997-2017 Trends, the average benzene concentrations at the Liberty Monitor are as listed in Table 2. Averaging only the available 2018 every third-day charcoal tube measurements gives a preliminary sense of the average benzene concentration for 2018.

More About Hydrogen Sulfide

Hydrogen sulfide has a Pennsylvania 24-hour standard of 0.005 parts per million (5 parts per billion). This air quality standard has frequently been exceeded at the Liberty monitor—on average about 53 times for years 2013-2017. That pace was slightly less with 12 violations through the fire and repair period ending on April 3, 2019, with some exceptionally high 24-hour averages as seen below.

Other Toxics and More

The Liberty charcoal tube samples described above for benzene also included analysis for toluene, ethylbenzene, mixed xylenes and naphthalene. Naphthalene is listed by EPA as possibly carcinogenic to humans.

Toluene, mixed xylenes and ethylbenzene have not been classified by EPA for carcinogenicity. Measurements at Liberty for the 24-hour charcoal tube samples in 2018 had no measurement for toluene, ethylbenzene or mixed xylenes above 3ppb and many measurements at zero. Naphthalene max day was .37 ppb with most measurements at zero. See ATSDR suggested limits below.

Glassport Monitor First Days of Fire and Repair (A different story)

The privately operated UV DOAS (Differential Optical Absorption Spectroscopy) monitor active at the ACHD Glassport monitoring site is a helpful temporary addition to the ACHD monitoring network since the 24-7 flaring was taking place just across the Monongahela River.

Among others, sulfur dioxide, benzene, ethylbenzene, toluene, p–xylene and naphthalene concentrations were tracked. Following are several charts taken from that data at the time of the fire and several days after included in a presentation at the ACHD’s Criteria Pollutant Subcommittee meeting on May 3, 2019. ACHD noted that “The operator presented this as final ‘adjusted’ data.”

The Clairton Coke facility fire and aftermath pollution brought many residents to community meetings to express health concerns and longstanding frustration with U.S. Steel facilities’ air pollution and regulatory noncompliance.

The Clairton facility was repaired and able to operate pollution control equipment earlier than expected on April 4. However, there remains enforcement actions, appeals, and several legal actions including the following:

1. Penn Environment, Inc. and Clean Air Council Civil Complaint against U.S. Steel Corporation can be found here:

2. Environmental Integrity Project, the Breathe Project and Clean Air Council, Notice of Intent to Sue United States Steel Corporation can be found here:

3. Citizens for Pennsylvania’s Future, GASP (not GASP in Allegheny County), Louisiana Bucket Brigade, and Sierra Club, filed a Complaint For Declaratory and Injunctive Relief against Andrew Wheeler, Administrator, U.S. Environmental Protection Agency, in his official capacity, can be found here: 4.

Details concerning U.S. Steel and active legal actions brought before the ACHD Hearing Officer can be found at ACHD Legal Docket:

What’s Next

Hopefully, the fire and its consequences were a wake-up call for United States Steel to implement a strong plan to achieve ongoing compliance with air quality standards at its Mon Valley facilities. Even before the fire new and more demanding coke oven regulations were in discussion at ACHD.

An answer to the noncompliance and community pollution complaints may be at least partially the new U.S. Steel upgrade proposal announced May 2, 2019. Procedurally, the plan will require permits, which will accompany public comment periods.

United States Steel, ACHD, and the public must resolutely determine that air quality compliance will be achieved. It is way past time for our region to have the healthy air quality that is required and that we deserve. Stay tuned for new data during the repair period.

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