Chemical process safety has become a widespread, international concern and receives high attention within the chemical industry. To improve process safety awareness, we publish short introductions into different process safety issues in cooperation with the monthly one-page Process Safety Beacon of the Center for Chemical Process Safety (CCPS).
Second Topic: Flammable Hydrogen-Air Mixtures
Hydrogen-air mixtures are explosive in concentrations from 4 to 75 % hydrogen. Air contains 21 % oxygen. With increasing oxygen concentration, the range becomes wider: In pure oxygen, the mixture is explosive from 4 to 94 % hydrogen. The required ignition energy is extremely low. Smaller volumes of hydrogen-air mixtures do not mean the danger of ignition becomes smaller.
Which statement is correct?
A spark you can barely feel, e.g., from a static discharge, has
a) about the same amount of energy as is needed to ignite a mixture of hydrogen and air.
b) about 50 times as much energy as is needed to ignite a mixture of hydrogen and air.
c) about 1000 times as much energy as is needed to ignite a mixture of hydrogen and air.
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