NEBOSH Practice Test

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What can cause a vapor cloud explosion?

Rainfall Impact
Vaporization of a Release
Strong Wind Patterns
Electrical Arcing

The correct answer is: Vaporization of a Release

A vapor cloud explosion can occur when flammable vapors, resulting from a release of liquid substances, accumulate in the air and reach an appropriate concentration. Vaporization is a critical factor in this process because it increases the surface area of the flammable liquid and allows more of its molecules to enter the vapor phase. When mixed with air in the right proportions and exposed to an ignition source, this vapor can ignite and lead to a rapid combustion event, typically characterized by a significant overpressure and explosion. In the context of the other options, while rainfall impact, strong wind patterns, and electrical arcing could influence safety conditions in hazardous environments, they do not play a direct role in initiating vapor cloud explosions. Rainfall may mitigate vapor concentrations by dispersing vapors, wind patterns may disperse vapors but do not cause explosions directly, and electrical arcing can ignite flammable vapors if they are already present, but it is the vaporization of substances that initiates the formation of those hazardous clouds in the first place. Thus, the process of vaporization is key to creating the potential for a vapor cloud explosion.