Fire Safety: Understanding, Preventing, and Extinguishing Fires

1. Origin of Fire

1.1. The Fire Tetrahedron

For a fire to occur, a chemical reaction between a fuel and an oxidizer is necessary, along with an activation energy. These three factors make up the fire triangle. The fire tetrahedron is formed by adding the chain reaction, which is a reaction that does not need external energy to be maintained.

• Fuel: A substance that reacts easily with an oxidizer to produce heat.
• Oxidizer: A substance that activates the fuel (e.g., oxygen).
• Activation Energy: The minimum energy required to initiate the combustion process.
• Chain Reaction: A self-sustaining reaction that does not require external energy.

Types of Fire

• Class A: Solid fuels like wood.
• Class B: Liquid or gas fuels like oil or acetylene.
• Class C: Electrical fires, such as short circuits.
• Class D: Metal fires, such as sodium.

2. Fire Extinguishing

2.1. Elimination of the Fire Tetrahedron

A fire can be extinguished by removing any of the components of the fire tetrahedron.

• Oxidizer:
  • Suffocation: Preventing oxygen from reaching the fire.
  • Modification: Replacing the air with an inert atmosphere like CO2 to displace oxygen.
• Activation Energy:
  • Cooling: Reducing the heat by applying substances that absorb energy through decomposition or a change of state.
• Fuel:
  • Removal: Cutting off the fuel supply to stop the fire from burning, for example, by closing a valve or turning off a pump.
• Chain Reaction:
  • Inhibition: Preventing the combustion particles from continuing to burn after the initial combustion (e.g., using flame retardants).

2.2. Extinguishing Agents

An extinguishing agent is a substance that acts on one or more points of the fire tetrahedron.

• Water: Cooling
• Dry Ice: Compressed gas that absorbs a large amount of heat during a change of state. (Suffocation and cooling)
• Foam: A mixture of bubbles, water, and a foaming agent. (Suffocation by covering the fuel and preventing air entry, and cooling)
• Dry Powder: A product that reacts upon contact with heat, leading to other products. (Cooling, smothering, and absorbing free radicals in the chain reaction)
• Halon: Very effective but not very clean. (Chain reaction inhibition, contains argon)
• Aerosols: An alternative method based on creating mists through the sublimation of solids and controlled combustion.

3. Fire Protection and Prevention

Structural Protection

Separating or securing dangerous areas to reduce fire hazards.

Alarms and Detectors

• Smoke Detectors: These detectors measure the current between two plates. A small deviation caused by combustion products decreases the current and activates the alarm.
• Photoelectric Smoke Detectors: These detectors operate based on the variation in light caused by smoke in its path.
• Heat Detectors: These detectors use a bimetal that bends when the temperature increases, closing a contact and activating the alarm.

Fire Safety Installations

• Fire Hose Reels: Equipped with a hose.
• Hydrants: Water hydrants without a hose.
• Portable Extinguishers: For small fires lasting less than 2 minutes. Should be placed no higher than 1.70m. There are pressurized (containing gas) and internal pressure types.
• Sprinklers: These devices release the extinguishing agent from above in the form of rain.
• Wet Riser Systems: These systems have constant water pressure. If a capsule breaks, the pump is activated, and water flows out. They must be replaced after each use.
• Dry Riser Systems: These systems have a detection system and an alarm that activates before the water is released.