Do you remember

Dana67Dart said

A guy I knew hauled chlorine in a standard sized van and had them.
Not sure why chlorine and static don't mix.

Here in Colorado the humiditiy gets so low I can shoot a 3/4" long spark from my finger tip to the metal around the door lock of our grand caravan just from sliding out of the front seat

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Chlorine dioxide vapor is unstable when the concentration in air is around 10% and the air pressure is higher than normal. A spark can cause explosive decomposition of the vapor. Hauling chlorine containers in an enclosed van could allow a build up of vapor if there was no adequate ventilation. The static strap was a good safety idea.