What is the fourth condition required for an explosion in a sewer when combustible gas, adequate oxygen, and sufficient heat are present?

What is the fourth condition required for an explosion in a sewer when combustible gas, adequate oxygen, and sufficient heat are present?

• A. Constant supply of combustible gas
• B. Enclosed area that will hold the gases
• C. Proper mixing of gas and oxygen
• D. None of the above

Answer: (C)

Mixing of the gas with the surrounding air is essential to form a combustible mixture. Even when you have fuel, enough oxygen, and a heat source, the reaction will not become explosive unless the fuel and air are blended in the right proportions so that ignition can propagate through the mixture. In a sewer, pockets of gas may be present without properly contacting oxygen in the proper ratio, so the flame cannot spread and trigger an explosion. When the gas and air mix correctly, and an ignition source is present, the confined space can convert that ignition into a rapid, explosive release of energy. The other conditions—a constant fuel supply or confinement alone—don’t guarantee explosion without that proper mixing.

Mixing of the gas with the surrounding air is essential to form a combustible mixture. Even when you have fuel, enough oxygen, and a heat source, the reaction will not become explosive unless the fuel and air are blended in the right proportions so that ignition can propagate through the mixture. In a sewer, pockets of gas may be present without properly contacting oxygen in the proper ratio, so the flame cannot spread and trigger an explosion. When the gas and air mix correctly, and an ignition source is present, the confined space can convert that ignition into a rapid, explosive release of energy. The other conditions—a constant fuel supply or confinement alone—don’t guarantee explosion without that proper mixing.