Fire Protection Systems: Detection Methods and Extinction Principles

Fire Detection Systems

The first phase and primary goal in fire protection is the detection itself. Fire detection means discovering the existence of a fire immediately after it has started. Detection can be achieved through two main methods:

• Human Detection

  This relies on continuous monitoring by personnel who, through our senses, can quickly detect the fire and transmit the alarm to initiate extinction procedures.

• Automatic Detection

  This is performed by devices called sensors (or detectors) that record the appearance of combustion products and transmit the information to a signaling box, which triggers the alarm and activates automatic suppression systems.

Types of Automatic Fire Detectors

The following types of detectors are commonly used in fire safety systems:

• Smoke Detectors

  These are suitable for slowly developing fires characterized in their early stages by smoke emission, often accompanied by very little heat. They may also be useful for fires that develop faster than their initial phase and produce considerable smoke and heat.

• Thermal Detectors

  These detect an increase in temperature. They are generally recommended only for fast-developing fires.

• Rate-of-Rise Thermal Detectors

  These indicate the appearance of a rapidly developing fire if the temperature increase per unit time exceeds a preset value.

• Ionization Detectors

  These detect visible and invisible gases and smoke, providing a wider field of application than standard smoke detectors.

• Optical Detectors

  These detect the infrared or ultraviolet radiation accompanying the flame.

Fire Extinction Principles

There are several forms of fire extinction, all based on the elimination of the sides of the Fire Tetrahedron (Fuel, Heat, Oxidizer, and Chain Reaction). Extinction measures focus, therefore, on actions targeting each of the factors involved:

Methods of Fire Suppression

• Action on Fuel (Starvation)

  This factor offers the most possibilities for action, such as substitution of the fuel source with products having a higher flashpoint, ventilation to eliminate the concentration of flammable vapors, refrigeration to keep the temperature below the ignition point, and the isolation of solid fuels.

• Action on Oxidizer (Smothering)

  Actions here are aimed at preventing the arrival of air (oxygen) at the surface of the fuel, which extinguishes the fire. Suffocation and modification of the environment—such as replacing the air atmosphere with an inert gas—are common examples of action on the oxidizer.

• Action on Heat (Cooling)

  This involves cooling the burning material, as absorbing a small amount of the heat generated by combustion is often sufficient to extinguish a fire. The utilization of water is the most common way to proceed with cooling.

• Action on the Chain Reaction (Inhibition)

  This method is based on projecting certain chemicals onto the fire that block the free radicals involved in the combustion process, causing the reaction to become inert.