By Matt Dempsey and Jordan Blum

Hurricane Harvey's winds and floodwaters have created emergencies at chemical facilities across the Houston area, from an Exxon Mobil roof collapse at its massive Baytown complex to the risk of an explosion at a chemical plant northeast of Houston.

The incidents, which also included a shelter-in-place Monday evening in La Porte from a pipeline leak, reveal how dangerous it can be when a storm of Harvey's magnitude collides with the nation's petrochemical capital. Even the controlled, Harvey-related shutdowns of refineries and plants are resulting in the release of millions of pounds of carbon monoxide and other chemicals into the region's atmosphere -- primarily through a process called flaring.

"This is an unprecedented storm, and we have taken every effort to minimize emissions and safely shut down equipment," said Exxon spokeswoman Charlotte Huffaker. "Flaring is an environmentally approved measure to safely burn hydrocarbons that cannot be processed during a unit shutdown. This is necessary so personnel can safely work on the equipment."

Several companies, including Exxon, have reported problems with storage tanks in recent days. In Exxon's case, a roof collapse triggered the release of more than 12,000 pounds of potentially toxic chemical compounds, according to a filing with the Texas Commission on Environmental Quality.

However, Exxon Mobil emphasized the collapse was partial and quickly brought under control. "The tank is now stable, and there are no containment issues," Huffaker added.

Northeast of Houston in Crosby, officials at an Arkema chemical plant are bracing themselves after multiple systems failed due to flooding.

Late Monday night, the facility lost power from both its primary supply and its backup generators. Employees moved highly volatile organic peroxides into back-up containers to keep them cool. If that class of chemical gets too hot, it can cause fires or explosions.

"At this time, while we do not believe there is any imminent danger, the potential for a chemical reaction leading to a fire and/or explosion within the site confines is real," Arkema spokeswoman Janet Smith said on Tuesday.

The Crosby Fire Department evacuated one employee last night and 11 remaining staff members were evacuated Tuesday afternoon when the refrigeration in some of the back-up containers also started to fail. State and local authorities began evacuating residents within a mile and a half of the plant Tuesday night.

Potential for harm

It would be surprising if Arkema had not considered a scenario like this, said Sam Mannan of Texas A&M University's Mary Kay O'Connor Process Safety Center. Companies can typically quench organic peroxides in situations like this with another chemical, to eliminate the danger.

"You'll lose the feedstock, but it's safer than letting it go into runaway mode," Mannan said.

The plant has been shut down since Friday in anticipation of the storm.

Both the Arkema plant in Crosby and the Exxon Mobil facility in Baytown were among the Houston-area sites with the highest potential for harm in an incident, according to a 2016 analysis by the O'Connor Process Safety Center and the Houston Chronicle. That analysis factored risks based on the amount and type of dangerous chemicals on site and their proximity to the public.

Arkema is working with the Department of Homeland Security and the state of Texas on a safe location for a command post to manage the situation.

In La Porte, a pipeline operated by Oklahoma-based Williams Cos. leaked dangerous chemicals Monday evening that triggered a shelter-in-place warning.

The leak was stopped that night, and no injuries were reported. Residents of La Porte, Shoreacres and Baytown were warned to close their windows and turn off their air conditioners. The Fred Hartman Bridge was closed over the Houston Ship Channel but has since reopened.

Williams Cos. officials said they will investigate the cause of the incident. The chemical that leaked, just north of the interchange between Texas 225 and Texas 146, was anhydrous hydrogen chloride, "which presents symptoms of eye, throat and nasal irritation," according to a statement issued by the city of La Porte. A federal safety guide identifies hydrogen chloride as a corrosive poison gas that "can cause serious or permanent injury." The nonflammable substance is used to manufacture "rubber, pharmaceuticals, chemicals and in gasoline refining and metals processing."

The Tulsa-based pipeline giant said the leak occurred at an "instrumentation rack" along a 14.5-mile system of 18-inch pipe that transports anhydrous hydrogen chloride gas.

Chemicals released

Nine other facilities have released some amount of chemicals due to Harvey, according to National Response Center data.

Nothing releases more emissions than the controlled shutdowns and restarts of refineries and chemical plants.

Emissions from Wednesday through Monday in the greater Houston area represent nearly 40 percent of the region's releases for all of 2016, based on pounds of chemicals, according to Luke Metzger, director of the advocacy group Environment Texas.

Roughly 2 million pounds of emissions have been released during Harvey-related shutdowns and incidents, compared to more than 5.2 million pounds all of last year.

Metzger argues these emissions are "illegal," because many exceed allowable limits.

He said the companies wait until the last minute to shut down plants, so they can collect as much money as possible, which creates more environmental hazards and emissions when the plants are shuttered more suddenly. These toxic emissions of carbon monoxide and other harmful chemicals can lead to increased cancer risks and respiratory problems, he argued.

(c)2017 the Houston Chronicle