What is chlorine gas, the plastic ingredient and chemical weapon that leaked into Brazosport in May?
by Rebekah F. Wood
Houston Chronicle
June 10, 2025
When chlorine gas seeped out of the massive industrial complex in Brazosport on May 20 and traveled downwind toward surrounding communities such as Clute, Lake Jackson and Richwood, some residents scrambled for details about the heavy, suffocating gas.
Chlorine is a powerful disinfectant, familiar to many for the smell that lifts off of public pools and cleaning products. In its gaseous form, chlorine is heavier than air. During a major accident, corrosive clouds of chlorine spread at ground level, and are toxic at high concentrations.
One of the deadliest chlorine accidents in modern history killed three people in Texas' rural Bexar County in June 2004 after a train crash released 60 tons of chlorine from a punctured tank car.
Here's what to know about chlorine gas and lessons learned from past accidents:
Can you see and smell chlorine gas?
Chlorine gas travels low to the ground in greenish-yellow clouds before gradually dispersing. It has an intense, bleach-like smell that can help warn people of a nearby leak. Since the gas is poisonous at high concentrations, authorities recommend sheltering in place during large leaks: shutting all windows and doors and turning off air conditioning systems to keep the gas out of your home or shelter.
What does chlorine gas do to your health?
Symptoms of chlorine gas exposure can include blurred vision, irritation of the eyes, nose, and throat, trouble breathing, nausea and respiratory failure, among others, according to U.S. health officials.
Concentrated chlorine gas attacks the lungs and can cause severe conditions such as toxic pneumonitis and pulmonary edemas.
Why was the gas used in chemical warfare?
Chlorine gas can kill. When French and Canadian soldiers first inhaled the gas in large doses after it was released by German troops during World War I, it irritated their lungs, triggering a choking effect. It was later used by Allied forces as well.
The chemical weapon was not only deadly, but also readily available due to its prevalence in the dye industry.
Now, chlorine gas is stored and transported in large quantities in the industrial areas around Houston and along the Gulf Coast. It is a key petrochemical component, serving as an ingredient in the production of plastics including polyvinyl chloride (PVC) and synthetic rubber, as well as chlorinated solvents.
Fumes rise from the train derailment near Loop 1604 and Nelson Road near San Antonio, Texas, Monday, June 28, 2004. The two freight trains collided, killing an engineer, sending clouds of chlorine gas and ammonium nitrate into the sky, derailing 40 cars and shutting down several blocks.
How do you protect yourself during a chlorine accident?
Officials often recommend staying indoors and "sheltering in place" during chemical emergencies. The deadly 2004 train crash in rural Bexar County illustrated the shortcomings of that strategy during major emergencies.
The EPA reviewed the incident and estimated that the chlorine leak near San Antonio reached concentrations that were nearly 900 times higher than fatal levels. Two residents who lived nearby were inside their home and called 911. Rescuers discovered their bodies hours later.
"Numerous local responders displayed bravery and professionalism in their efforts, as well as a sincere effort to assist trapped and wounded citizens," the EPA found. But officials said there was no way to save the victims near the site of the crash.
How serious was the chlorine leak in Brazoria County?
The industrial accident in Brazoria County wasn't as severe as the leak from the 2004 train crash. Records filed with state regulators show that more than 8,000 pounds of chlorine leaked. The punctured tank car in Bexar County released 60 tons of chlorine.
Still, data reviewed by the Houston Chronicle shows the recent leak was the most chlorine released accidentally in Texas in at least five years. One worker was treated at a hospital and released, and local residents raised concerns that they weren't immediately warned of the danger.
“Until I looked on our local Facebook channel, I didn’t even know anything about it,” said Gary Witt, a retired Surfside Beach resident who chairs the environmental group Better Brazoria.
