Energy & Environment

After An Explosion, How Do Houston First Responders Know If The Air Is Safe?

How the city responds to major air quality incidents, and what to expect if it happens near you.

City officials brief reporters after an explosion on Jan. 24.

Two weeks ago, a massive explosion at an industrial facility in Northwest Houston killed two people and damaged hundreds of nearby homes. But with that destruction came a question: how safe was the air thousands of people were breathing?

Immediately following the explosion, 18 people self-reported to emergency rooms with minor injuries like breathing problems, according to the Houston Fire Department. Investigators confirmed the fuel was propylene, a gas that can be detected by its smell, which likely reacted to the building’s electrical system to cause the explosion at the Watson Grinding and Manufacturing facility.

Because of a state law, emergency responders in Houston often have no idea what chemicals are stored on site. So how do they know if the air is safe, and when do they know for sure?

In the case of last month’s explosion, Houston Fire Chief Samuel Peña said the fire department was the first to arrive on the scene, and immediately tested the air’s safety.

"Before they began offensive operations," Peña said, "the first thing they're going to be doing is monitoring the atmosphere. And we felt confident that the atmosphere was safe to breathe."

The department's Hazmat team, using handheld monitors that detect dangerous gases, began testing around 5:45 a.m., a little more than an hour after the explosion.

"What they told me is, ‘We're not getting any negative readings, any hazardous readings,’" Peña said. "I don't know what the levels were or what they were getting as far as oxygen but I can tell you that it was safe for us to operate without any specific and special equipment in that scene."

The explosion aftermath at Watson Grinding & Manufacturing Co.

What were they looking for in the air?

Rather than monitor for specific chemicals, Peña said responders monitor for “explosive levels.”

The HFD Hazmat team monitored for five different levels at the Watson Grinding and Manufacturing facility: lower explosive limit, carbon monoxide, volatile organic compounds, hydrogen sulfide, and oxygen. After that testing, the fire department tweeted there was no need to evacuate, and later, the city tweeted there were no significant problems with air quality in the area.

By 9 a.m., the Health Department arrived to do more air quality monitoring using a van called a Mobile Ambient Air Monitoring Laboratory. That was almost five hours after the explosion.

"The Volatile Organic Chemicals (VOCs) measured by the MAAML were all low with only traces of propylene observed (1 – 2 ppb) with nothing significant that is not normally present (like traces of BTEX and ethanol from vehicle traffic) that would adversely impact resident health in the area,” Health Department spokesperson Porfirio Villarreal told Houston Public Media, four days after the incident.

The Houston Fire Department and the Health Department didn't share their air quality monitoring data with the public on the day of the explosion, but made information available by request days later. Other agencies arrived to test air quality, too — the Texas Commission on Environmental Quality and Harris County's Pollution Control Department. While TCEQ has not released data, a spokesperson said that information is available by request, while an HCPCD spokesperson said that agency’s data will be released within weeks.

Environmental advocates argue there’s demand for that information to be available sooner.

"The public has a right to know about pollution hazards and potential health risks in a timely manner,” said Matthew Tresaugue, senior communications manager with the Environmental Defense Fund.

Around eight hours after the explosion, Air Alliance Houston executive director Bakeyah Nelson told Houston Public Media, "Based on what we know right now there would not be necessarily any air quality concerns but it is a chemical safety risk. But that's just based on what we know now, which is not much."

At that point, her advice was: "If you don't have to be in that area, don't be in the area.”

Risk across the city

The Houston area has hundreds of industrial facilities storing chemicals, and sometimes, like in this case, they're right next to residential neighborhoods.

At a Houston City Council meeting days after the explosion, District H representative Karla Cisneros said there's a chemical facility she passes every day, and she can't help wondering how safe it is.

"Because something that's right there in such an urban area, it would blow up the highway possibly and destroy neighborhoods, maybe poison us,” Cisneros said. “I think we have situations possibly all over our city that we need to understand.”

Councilmember Amy Peck, who represents the neighborhood where the explosion happened, recalled a fire in the Spring Branch area in 2016 at a facility that stored 500 gallons of pesticides.

"This isn't even the first disaster like this that we've seen in District A over the last couple of years," Peck said.

According to Tresaugue, of the Environmental Defense Fund, around 200 industrial facilities in Harris County are required to have emergency risk plans on file. The Watson Grinding and Manufacturing facility that exploded two weeks ago wasn't one of them, because the requirement only applies to facilities with a greater amount of product on site.

But it had enough product to damage nearly 500 buildings,” Tresaugue said, “so something's wrong with that."

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