Portable Fire Extinguishers
Portable fire extinguishers include both self-contained fire extinguishing equipment that can be carried by one person and wheeled units that can be handled by one or two people. Due to their limited capacity, portable fire extinguishers are designed to control fires that are just starting or that are of limited size.
Portable fire extinguishers need to be located near the equipment to be protected, but not so close that they can become involved in the fire or that a person cannot reach them. The suggested distance from their point of use is between 5 and 15 m.
From any grade-level point in a process plant, the maximum horizontal distance to a dry chemical extinguisher should not exceed 15 m. Extinguisher locations should be conspicuous, clearly marked, and visible from several directions. The locations should not be blocked with materials or equipment that might conceal or impede access to them.
The superior cooling capacity of water over other extinguishing agents makes it particularly effective on fires involving ordinary combustibles such as wood, paper, fabrics, or rubber. Water extinguishers do not require extensive cleanup after use and they are non-corrosive to electronic circuitry, unlike dry chemical extinguishers. When water extinguishers are subject to freezing weather antifreeze is added.
Carbon dioxide extinguishers
Carbon dioxide (CO2) is stored in extinguishers in the liquid phase. It vaporizes when released thereby smothering a fire by excluding the air (oxygen) needed for combustion.
As already noted, Carbon dioxide extinguishers are preferable to water or dry chemical extinguishers where water damage and fouling of delicate electrical, electronic, or laboratory equipment cannot be tolerated or where cleanup is a consideration.
If a CO2 extinguisher is discharged in a confined space then that space must be ventilated once the fire is extinguished.
Dry chemical extinguishers
Many types of dry chemical extinguishing agents are available. Those shown below are used in the process industries.
▪ Sodium bicarbonate;
▪ Potassium bicarbonate base (Purple K); and
▪ Monoammonium phosphate.
Sodium bicarbonate was the original dry chemical extinguishing agent. The chemical currently available is a mixture consisting primarily of sodium bicarbonate with various additives to improve flow and storage characteristics. Chief among the additives is a silicone polymer. It is used to prevent moisture absorption and consequent caking of chemicals.
It works by interrupting the propagation of the flame. Its electrical resistivity is high, and it is nontoxic. This agent may be used for extinguishing fires involving flammable liquids, gases, and electrical equipment. It is not effective in extinguishing deep-seated fires in ordinary combustibles.
Potassium bicarbonate chemical, whose physical properties are similar to sodium bicarbonate, is effective at extinguishing fires involving flammable liquids and gases. It is also suitable for use on fires involving electrical equipment. It is not effective in extinguishing deep-seated fires in ordinary combustibles.
Fire equipment service
Monoammonium phosphate-based chemical is effective in controlling and extinguishing fires involving flammable liquids and gases, ordinary combustible materials, and electrical equipment.
It is recommended where piped water is not available, where freezing conditions are expected, or where a combination of different classes of hazards exists. It has physical properties similar to the sodium bicarbonate chemical but is more effective on flammable liquid fires.
It is corrosive to electronic circuitry. It should not be mixed with bicarbonate dry chemicals. A chemical reaction can occur in the extinguisher that generates CO2 and other gases; the pressure buildup could rupture the extinguisher.