Massive Leak of Liquified Chlorine Gas - (Henderson, Nevada - May 6, 1991) » Expanding Gas Cloud

It was very difficult to accurately predict the size or travel of the gas cloud resulting from vaporization of the liquid pool on the ground. The flow rate of the leak could not be determined and the size of the resulting liquid pool could not be observed, since the storage tanks are surrounded by other processing equipment. The developing cloud could not be visually monitored due to the darkness and the location of the problem within the facility.

The heavier-than-air chlorine vapors have a tendency to move along the ground and concentrate in low spots. The BMI complex is located in a relatively high area and the terrain slopes down toward the north for several miles. A dry wash provided a low path for the heaviest concentration to migrate into a sparsely populated area north of the BMI complex A growing cloud of lower chlorine concentration covered an expanding area along the ground. The wind was unusually calm and slowly pushed this cloud in the uphill direction, toward the Command Post and toward more populated areas to the east and west. Indications are that the gas cloud simply expanded under the cool and dry atmospheric conditions and moved slowly over the general area, while the amount of vaporized chlorine in the atmosphere continued to increase.

Weather Conditions:
Temperature 65°F
Relative Humidity 15%
Wind 0-5 mph, variable direction

As time progressed it became evident that the chlorine cloud was continuing to grow. Subsequent investigation showed that the corrosive properties of the liquid had damaged the valve on the discharge side of the transfer pump, allowing a continuous supply of chlorine from the contaminated storage tank to reach the leak. The leak also increased in flow rate, as the corrosive properties of the liquid ate a growing hole in the steel elbow. These factors created a pool of liquid, which allowed increasing quantities of chlorine to vaporize into the atmosphere. Before the leak was stopped an estimated 70 tons of liquified chlorine gas escaped, making this one of the largest recorded leaks of this type in the United States.

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