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Chlorine Gas Release

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Michael Fox, PhD.



Chlorine Gas Release

A swimming pool technician at a high school was changing over chlorine (gas) cylinders when allegedly the empty chlorine cylinder valve would not close. As a result, the pool technician was exposed to chlorine gas and he claimed inhalation injuries. Chemaxx was hired to investigate this incident.

There was some uncertainty whether the first responders were able to shut off the chlorine valve. Nevertheless, the chlorine cylinder was placed into a salvage cylinder, sometimes referred to as a coffin. The heavy corrosion on the outside of the cylinder when it was removed suggests that it was leaking chlorine when it was put into the coffin. In fact, the valve on chlorine cylinder was found to be wide open when it was removed from the coffin, suggesting that the pool tech or first responders had turned the valve the wrong way. Instead of closing the valve he had opened it.

When the valve was removed from the cylinder and tested using 500-psig nitrogen pressure it was found to be perfectly gas tight. A soap film remained intact over the outlet of the valve while the inlet pressure was 500-psig, as seen in the photo below.

A witness at the high school had testified to seeing frost on the lower portion of the chlorine cylinder. Such frost would develop if there is evaporating liquid remaining in the cylinder, which in turn meant that the cylinder was not empty. In other words, the pool technician may have thought the cylinder was empty when in fact it was not. This human error may have contributed to the incident.

To verify the formation of frost, Chemaxx conducted chlorine release experiments under controlled conditions, as seen in the photo below.

In the chlorine-frost experiments the weight of the cylinder was measured versus time together with the temperature near the bottom. Two thermocouples were attached at two locations from the bottom of the cylinder. The figure below illustrates the changes in temperature and weight loss with time.

While the case went to trial and the jury found for the plaintiff, the relatively low award was less than what the chlorine company had been willing to settle for before the trial.

Dr. Fox has his Ph.D. in Physical Chemistry and is a Certified Fire & Explosion Investigator with substantial experience investigating complex industrial chemical accidents, fires and explosions as well as chemical-related consumer produce accidents, fires and explosions. He is also a Certified Team Leader in OSHA Process Hazard Analysis.