Immediate Response to a Vapor Release


In my discussions to do with the Highly Hazardous Chemicals that are being transported through Ashland it has become evident that many people are not aware of the immediate actions to take should there be a release of a toxic gas such as chlorine.

Suggested Responses

Here are some thoughts as to what to do in such a situation.

Move Across the Cloud

As the gas escapes from the release point it forms a cloud such as that shown in the sketch above. Inside the cloud boundary the concentration of gas is high enough to have an unacceptable effect on human health — outside the boundary the gas may be detectable but it should not affect have a long-term effect on the health person involved.

This means that, if you are inside the toxic envelope, the best thing to do is not to move downwind as many people think but to move at 90° to the cloud — that way you leave the affected area as quickly as possible.

Move Indoors

If you are in a near a building a good response is to move indoors, close all doors and windows and turn off the air conditioning. A rule of thumb is that a normal building will reduce the concentration of gas by a factor ten. So, if the concentration of the gas outside is 100 ppm (parts per million) it can be as low as 10 ppm indoors. Then wait for say 20 minutes.


In this clip we see a release of chlorine gas — evidently from a ruptured hose. The gas affected people many hundreds of yards away, although there do not appear to have been fatalities.

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