Question

Which type of fire protection is required for vapor explosion?

• A. Fire hydrant system
• B. Sprinkler system
• C. Water mist fire protection systems
• D. Portable fire extinguisher

Hint:

\textbf{Vapor explosion} risks occur with flammable gases/vapors.
Fire protection for such hazards needs to address rapid flame spread and potential for re-ignition.
\textbf{Water mist systems} create fine water droplets that provide rapid cooling, oxygen displacement, and radiant heat blocking. They are effective for Class B fires (flammable liquids/gases) and can mitigate some vapor cloud fire scenarios.
Conventional sprinklers might be less effective for rapid vapor cloud events. Hydrants and portable extinguishers are for manual firefighting of established/small fires.

Answer 1

The Correct Option is C

A vapor explosion (or more precisely, a vapor cloud explosion - VCE, if it's an unconfined cloud) occurs when a significant amount of flammable vapor or gas is released, mixes with air to form a flammable mixture, and is then ignited. This results in a rapid combustion that can generate a high-pressure blast wave. Protecting against vapor explosions involves preventing their occurrence (e.g., controlling leaks, ventilation) and mitigating their effects if they do occur. Fire protection systems for areas with vapor explosion risks need to be carefully chosen. Let's evaluate the options:
(a) Fire hydrant system: Hydrants provide large volumes of water for manual firefighting by trained personnel using hoses. While useful for fighting established fires that might *result* from an explosion or cause one, they are not a primary preventative or rapid suppression system for the explosion event itself.
(b) Sprinkler system: Conventional sprinkler systems discharge water droplets to control or suppress fires by cooling and wetting fuel. They are effective for Class A fires (ordinary combustibles) and some Class B fires. However, for a rapid vapor cloud ignition, their response time and water droplet size might not be optimal for mitigating the explosion or a resulting flash fire effectively. Water can also sometimes spread flammable liquid fires.
(c) Water mist fire protection systems: Water mist systems discharge very fine water droplets (mist). These systems have several advantages for certain hazards, including:
Cooling: The large surface area of fine droplets allows for rapid evaporation and significant cooling of the flame and surrounding air.
Oxygen displacement/dilution: The steam generated by evaporating mist can displace or dilute oxygen, inhibiting combustion.
Radiant heat blocking: The mist can block radiant heat. For flammable liquid fires (Class B) and some gas fires/explosions, water mist systems can be very effective. They can rapidly cool, inert the atmosphere locally, and suppress flames. They are particularly considered for applications like machinery spaces, turbine enclosures, and areas with flammable liquids or gases where vapor cloud formation is a risk. Their ability to rapidly absorb heat and dilute oxygen makes them suitable for mitigating certain types of vapor cloud fires or preventing escalation.
(d) Portable fire extinguisher: These are for first-aid firefighting of small, incipient fires. They are not adequate for dealing with a vapor explosion hazard or a large resulting fire. For protection against fires resulting from or leading to vapor explosions, especially in enclosed or semi-enclosed spaces involving flammable liquids or gases, Water mist fire protection systems are increasingly recognized as an effective technology due to their rapid cooling, oxygen displacement, and efficient use of water. They can be designed for total flooding or local application. Given the options, water mist systems are the most specialized and suitable for certain types of vapor explosion hazards or associated Class B fires among those listed. \[ \boxed{\text{Water mist fire protection systems}} \]