Plant Fire Safety - Fire Prevention Methods PDF

Plant Fire Safety • Chapter 4 OBJECTIVE 4 Discuss fire prevention methods for the five classes of fires. METHODS OF PREVENTING THE FIVE DIFFERENT TYPES OF FIRES Class A Fire Prevention To prevent a Class A fire from starting, there are a number of additional measures, as well as, the general me...

Plant Fire Safety • Chapter 4 OBJECTIVE 4 Discuss fire prevention methods for the five classes of fires. METHODS OF PREVENTING THE FIVE DIFFERENT TYPES OF FIRES Class A Fire Prevention To prevent a Class A fire from starting, there are a number of additional measures, as well as, the general methods mentioned above that can be applied: a) ( Regular cleaning is an effective method of removing accumulations of Class A type material so that it does not build up to a combustible volume. Class A material is of particular importance to the Power Engineer in plants such as pulp mills, sawmills, and coal-fired plants, where the fuel is a Class A material. Fuel can accumulate in various locations of the plant (such as alongside conveyors, at tripper floors, and atop bunkers). Regular sweeping, vacuuming, mopping, hosing and washing are key to preventing Class A fires. b) Hose any vulnerable areas down regularly. Even if regular cleaning occurs, areas that are inaccessible to sweeping and cleaning can exist. A useful method of removing the buildup of Class A material is to hose down the area. Water not only washes away Class A material, but it also wets down any remaining material, thus reducing the likelihood of ignition. One should first ensure that equipment in the area is protected from water with barriers or covers before the hose is turned on. Some areas cannot be hosed down, such as any opening into a black liquor recovery boiler. A devastating explosion could occur if water gets into the furnace of a black liquor recovery boiler. A hose accidentally aimed at an open port into a furnace can be a life threatening condition. c) When there is possible exposure to an ignition source, clothing should be fire-rated. This applies particularly to those working around boilers or other sources of heat, such as welders. d) Install sprinklers in areas that have Class A material. Water is extremely effective in putting out Class A fires. Sprinlders react automatically to extinguish fires, and to prevent fires from getting larger. Class B Fire Prevention Oils and greases are most effectively prevented from igniting by separating the fuel from the ignition source and by keeping the fuel from coming into contact with air (oxygen). Some methods are: a) Maintain fuel-containing pipelines. Leaking valve packing, screwed fittings and gaskets permit Class B materials to contact air. Leaks must be identified and immediately repaired. Puddles must be absorbed and the absorbent properly disposed of. b) If clothes have come in contact with oil or grease, be aware that they can be flammable. Also, clothes- coveralls, for example- for laundry should be stored properly. Coveralls may no longer be flame retardant if they have become covered with grease, oil, or even insect repellent. Spontaneous combustion with oily clothes - or rags - can occur if they are left in a pile and exposed to the air. Laundry services have been known to have piles of clothes burn, and ignite in dryers even after they have been washed. Piles of rags used in work with oil and being discarded can also spontaneously combust. Store oily clothes and rags in proper storage or disposal areas. 4th Class Edition 3 • Part A 4-23 Unit A-4 • Introduction to Plant and Fire Safety ================== c) ================== Oil storage tanks and lines must be constructed according to code. Fuel storage tanks are vented to the air to permit changes in the tank volume as fuel is withdrawn, added, or changes in volume with temperature. The tank must not be exposed to any ignition source, especially near the vent. Note that safety codes require that any temporary sources of ignition such as welding near the vent is not permitted. Welding or cutting a tank that has contained fuel is a dangerous and usually prohibited practice, as the tanks can absorb fuel and explode. Fuel tanks are also required to have a berm or spill container that will hold the entire contents of the tank in the case of a leak. Fuel tanks can also be constructed with double walls with detection devices between the two walls to detect any leaks from the inside container. Oil containers should be stored away from ignition on a platform that has a large enough reservoir to hold a leak or spills. ( d) Oil or grease spills or leaks should be cleaned up. A buildup of grease for example around grease nipple can be ignited by an overheated bearing or welding spatter. Grease or oil dripping down to a lower area can also be susceptible to ignition. e) Grease, oil, and tools such as grease guns and pumps should be stored in proper areas. Flammable materials such as greases, oil barrels, and other related equipment should be stored in vented buildings at a safe distance from other buildings and areas. f) Of particular importance to a Power Engineer is that the boiler fuel oil systems near the burner be kept free from oil. Oil guns are inserted and removed from boilers regularly, and drips and spills are common. It is not unusual to have trays containing absorbent material located under the burner guns. This also includes areas where the guns will be cleaned and serviced. Class C Fire Prevention Class C fires become Class A and Class B fires once the electrical power is turned off. Class C electrical fires start when the ignition source - the heat due to over-current or electrical arc ignites the flammable material it is in contact with. To prevent these conditions from occurring: a) All electrical installations must follow electrical code so that overheating and arcing do not occur. Power Engineers should ensure that electrical tradespeople have installation permits, and that the equipment is inspected before being placed in service. b) Ensure all electrical equipment purchased, installed, or used on site is approved by CSA, ULC or some other accepted approval agency. Power Engineers can look for approval stamps or labels on the equipment nameplate of portable electric power tools, extension cords, appliances, and lighting. c) Do not put flammable material on or near electrical equipment. For example, do not store small lubricating oil cans or paper towels in a breaker panel or in the electrical room. d) Regular inspections should occur to ensure there is no damage to electrical equipment. Electrical cords should be checked for wear and are either repaired or replaced. Motors should be cleaned of dust accumulations. e) If necessary covers and protection barriers should be installed over electrical equipment. Breakers and motor control centres should be protected from lealdng water or other fluids. If water may be present outside of an electrical room then there should be a lip at the bottom of the door to act as a dam to prevent water from lealdng under the door. Water services should not be installed near electrical equipment. f) 4-24 Operators should be trained to safely operate the main breaker and electrical isolation switches. During an emergency, a Power Engineer may be required to electrically isolate certain areas of the plant. 7 E--------------------------- s:: 4th Class Edition 3 • Part A ( Plant Fire Safety • Chapter 4 Preventing Fires in Areas having Electrical Classifications Class I electrical equipment must be designed to be fire safe in any area where there may be the presence of flammable gases or vapours. To prevent fires from occurring within a Class 1 designated area, electrical equipment (even portable equipment) such as lights, switches, breakers and controllers must be of an acceptable explosion proof design and be hermetically sealed or immersed in oil, so that the electricity cannot ignite an explosive atmosphere. Class II locations are concerned with the presence of combustible dusts that can exist in explosive concentrations. To prevent fires from burning in these dusty areas the electrical equipment should be contained in dust tight enclosures. Lights or lamps should be designed to accumulate minimal amounts of dust, be protected from damage by an acceptable guard or by location, and clearly marked to indicate wattage. Class III locations involve the presence of airborne material fibers that are easily ignited. To prevent a Class III location fire, the motors, lamps, switches, circuit breakers, controllers and other electrical equipment must be enclosed with tight covers. Lights and lamps must have their wattage clearly marked. Class D Fire Prevention It is unlikely that the average Power Engineer will encounter a Class D fire. However, if combustible metals exist in the plant, operators need specialized training to fight Class D fires. Training must address the specific metals that are on-site, because particular combustible metals require particular extinguishing materials. The Power Engineer should be familiar with how to prevent Class D fires from occurring. Some measures include: a) Store combustible metals away from potential ignition sources. Ignition sources could be traditional heat sources, or materials that may react with and ignite a combustible metal. Such a reaction would arise from contact between a specific metal and a specific reactant (such as sodium and water). Therefore, it is necessary to understand the reactivity of a particular metal with a particular substance, and to keep the two substances far from each other. The material would have to be identified by an individual familiar with the metal in question, who can determine which specific material is to be kept from the metal. b) Signage should be in place that states what combustible metal is being stored and what materials cannot be stored near the metal. Class K Fire Prevention A Class K fire involves kitchen greases and oils that burn at high temperature. While essentially a Class B fire, the type of oil and grease used in kitchens and the dangerous conditions under which they are used (large open containers of heated oil) increase the likelihood of a large and destructive fire. To prevent Class K fires: a) Turn off electric power to the oil and grease heating elements when not in use. b) Do not leave heated oil workstations unattended, even when first warming the oil. c) Continually monitor the temperature of the oil while the cooking station is in use. d) Fill the oil and grease reservoirs when they are cool. This will protect the individual from being splashed, and it will reduce the possibility of ignition. e) Cover the oil and grease containers with metal covers to prevent any ignition sources from falling into the oil. 4th Class Edition 3 • Part A 4-25 Unit A-4 • Introduction to Plant and Fire Safety ================== ================== CHAPTER SUMMARY It is important to understand the types of fires and how they burn in order to be able to prevent them. Different classes of fuels require different preventative measures to reduce the possibility of fire. The Power Engineer or other workers on site should: a) Be able to determine which one of the five classes of fire they are dealing with. b) Know what fire preventative methods are available. c) Be able to apply preventative measures effectively. Recall that fires have both a reducing agent and an oxidizing agent that interact to create a fire. The fire tetrahedron explains how a fire continues to burn. The four elements are fuel, oxygen, ignition and a self sustaining uninhibited chain reaction. If any one of these elements is removed, a fire cannot start, and an existing fire cannot continue to burn. Once the student understands the basics of how a fire can occur, methods of preventing these different classes of fires can be implemented. There are standard preventative measures such as restricting areas as no smoldng, cleaning the area, or removing flammable materials to a safe area. Power Engineers should also recognize that they handle combustible material as a regular part of their job - not just the fuel for the boiler, but also other combustible materials on the worksite. As a result, Power Engineers must pay greater attention to possible fire conditions. Power Engineers must understand how electricity can ignite combustibles in various hazardous locations. Recognizing the consequences of what can happen when there is a blow back from a balanced draft boiler, or storing oil and grease in an outside enclosure away from ignition sources are extra situations that the Power Engineer should be trained in. These and others mentioned in this chapter are effective methods of preventing fires from happening. 4-26 <(------------------------------4 -th__ C-Ia_ss__E_ d_ mo_n__ 3· __P_a_ rl_A _