In Tulare, Calif., the chlorine concentrations at the recycling plant were extremely high. Three hours after it happened, the Visalia Fire Department measured the gas at 328 parts per million near the tank. It was probably much higher when the workers were trying to escape. Studies show 40-60 ppm produces lung injury; 430 ppm usually causes death in 30 minutes, and 1,000 ppm is fatal within a few minutes. Under federal standards, workers are never supposed to be exposed to concentrations exceeding 1 ppm.
"Exposure to high levels of chlorine gas from a release can cause severe health effects, including death," said Mary Anne Duncan, an epidemiologist at the federal Agency for Toxic Substances and Disease Registry who has assisted with the aftermath of several chlorine accidents, including the one in Tulare.
Erik Svendsen, who studied the health effects of the Graniteville chlorine cloud, said researchers knew they would find pulmonary and other health problems in people exposed. But they found a lot of Post Traumatic Stress Disorders, too.
"Chlorine was used as a war gas for a reason. It was designed not just to kill the enemy but also to inflict fear in the enemy. You remember every second you were exposed to the gas. You don't know where to go. You see your clothes bleach before your very eyes. You see animals die,” said Svendsen, a Tulane University epidemiologist.
“It's not just a toxic event. It's a traumatic event. You're powerless. You're being exposed to something you can't stop. You have a metabolic stress response that has effects on the body physiologically.”
Only four months before the accident in Tulare, five workers were injured at another California recycler, U.S. Metal in Indio, when a crane worker pierced a cylinder tank and set off an explosive chlorine gas release.
And in July, at Tyson Foods Inc., in Springdale, Ark., chlorine gas was released after the accidental mixing of two chemicals, exposing 173 people and sending 50 to hospitals, including five that wound up in intensive care. Chlorine is used in the company’s sanitizing washes.
Across the country, data going back to 1993 show that chlorine accidents occur in the United States at the rate of at least once every two or three days, and about one-third of them cause injuries.
In 2009 alone, chlorine was involved in 181 reported accidents with 56 resulting in injuries, based on the latest report from a federal database called Hazardous Substances Emergency Events Surveillance (HSEES). That amounts to 3.8 percent of all the reported chemical emergencies that year. Chlorine had a high percentage with victims, 30.9 percent, second only to carbon monoxide, which had 41.7 percent with victims. Roughly one-third of the states reported, and only for a part of the year, so the real number of accidents and injuries is much higher, experts say.
“Chlorine releases in fixed facilities resulted in victims and evacuations in more industry categories than any other substance," says a 2004 study by researchers from the Agency for Toxic Substances and Disease Registry. That study was based on HSEES data of 40,000 chemical incidents from 1996 through 2001.
Accidents involving chlorine "were more likely to result in events with victims, evacuations and decontaminations when compared with non-chlorine events,” according to another study by the same federal agency published in 2002.
Of 865 events involving chlorine alone between 1993 and 2000, 275 caused injuries, the study says. Of the 1,071 victims, 759 were workers, 235 were members of the public and most of the rest were first responders.
Transporting chlorine also poses more risks than other substances. The U.S. Department of Transportation issued a report last month weighting the most serious accidents in terms of deaths and major injuries from 2005 to 2009. Chlorine led the list with 83 major injuries and nine fatalities out of 48 rail and road accidents compared to gasoline, second on the list, which had 19 major injuries and 30 fatalities out of 1,306 rail and road accidents.