Protecting Employees from the Effects of Dust Explosions and Fires in the Die Casting Industry INTRODUCTION This paper discusses the prevention and/or control of fires and explosions when working around die casting facilities producing white metal castings. Topics included are: Key Facts You Should Know Emergency Plans and Procedures Clothing Fires Housekeeping Control of Ignition Sources Control of Combustible Materials Removal of combustible metal waste Inspection and Maintenance Fire Extinguishing Agents Controlling Metal Fires Fire Fighting Organization Automatic Sprinkler Protection The intent is to assist in implementing work practices and procedures necessary for dust explosion and fire safety at the plant. The practices and procedures discussed here are adapted from NFPA 484 - Standard for Combustible Metals, 2006 Edition. Some of the practices and procedures that are of greatest concern are appropriate housekeeping, fugitive dust control and safe handling of fine particles. This document has been prepared as part of the North American Die Casting Association course on combustible dust in the die casting Industry. KEY FACTS YOU SHOULD KNOW This section presents some key information regarding combustible metal and dust operations – the materials used in the die casting industry. Some of this information is unusual and not widely known. Health and safety depends on the recognition of actual or potential hazards of combustible metals, particularly metal dusts; the control or removal of these hazards; and, training of employees on safe working procedures. Important guidance on health and safety is found in NFPA 484 Standard for Combustible metals. Everyone working with combustible die casting metals, (particularly in the form of dusts and fines) needs to know some key facts. Emergency response and preparedness are especially important. Containers for molten metal must be cleaned and dried prior to receiving the molten material. Metal pieces charged into liquid molten metal must be clean and dry. Water wet containers and charge pieces can cause a molten metal explosion When combustible metals burn, an intense, extremely hot, orange or orange and white flame is produced. This is accompanied by a large volume of white and gray smoke. If the burning metal has been contaminated with water, fire will be more intense. Water and Other Common Fire Extinguishing Media Water does not mix with burning combustible metals. The intensity of the burning will break the water into oxygen and hydrogen and greatly increase the heat and energy being released by the fire. Explosions have been produced by applying water to burning combustible metal. Carbon dioxide has a similar effect in that it breaks down into carbon and oxygen. Most combustible metals will burn in 100% carbon dioxide. Halon type and other halogenated extinguishing agents may decompose into hazardous products and are not suitable for use on die casting metal fires. Dry chemical extinguishers may be used on burning flammable or combustible liquids are mixed with combustible metal but have not started the metal to burn. Fines, Chips and Ingots Dusts, fines and powders produced from die casting metals may cause explosions. If these materials are in a confined space, the concentration of particles may be higher and more likely to explode. Chips and turnings ignite with a very hot flame. If they are coated with cutting oil or other petroleum product, there may be a tendency to ignite spontaneously. Heavy wall die castings, thick bars and ingots are difficult to ignite or may not ignite at all. If ordinary combustibles are burning and heat up these heavy materials, especially magnesium alloys, the heavy items may participate in the fire in a spectacular fashion. Burning combustible metals produce an unusual amount of heat. Such a fire may cause water to come out of concrete (the water of hydration in the concrete) or even rocks. This water may cause increased burning, burst the materials and cause pieces of rock or concrete to be thrown about. Asphalt paving material can be involved in the fire because of the intense heat given off. Fires in die casting metals cannot be directly extinguished. They may be controlled and separated from the oxygen in air, cease burning and cool. In die casting metal fires, this is done by applying dry extinguishing agents to completely cover the burning materials. 2 Combustible metal dusts, and fines create unique hazards. If they contain or are contacted by moisture, they can produce hydrogen, a flammable gas; oxygen, an oxidizer and heat. This can cause an explosion or fire. Thermite Reactions Magnesium, aluminum (or a similar light metal or alloy) dust, not oxidized, can react in contact with rusty iron and produce heat in what is called a thermite reaction. Specially made tools are used to avoid this and friction sparking. Thermite reactions can be an ignition source. Thermite sparking was identified as a hazard in coal mines in the 1940s. Articles made from light alloys that accidentally hit, or were dropped on, steel structures or machinery caused a spark. Magnesium and iron powder mixtures have been used to demonstrate this reaction in chemistry labs, a spectacular show. Equipment to Remove Containers Storage areas for containers of combustible metal are to be equipped with material handling equipment that would enable a container to be removed from the area quickly and efficiently in and emergency. Hydrogen from Moist Particles Stored die casting metal dusts, chips and particles that contain moisture can produce hydrogen gas. A significant amount of hydrogen produced in the storage area can produce a Class I, Group B hazardous location. Ignition sources must be excluded and good ventilation provided. Flammable and Combustible Liquids Use of flammable and combustible liquids must comply with OSHA 29 CFR 1910.106 and NFPA 30. Consider: • Spray finishing; • Open containers; • Spills; • Use around ignition sources; • Lack of ventilation. High capacity hydraulic systems (greater than 50 gallons), must use hydraulic oil with a flashpoint exceeding 200° F. These systems are often used in powering and controlling heavy grinders, forging equipment and large milling machines. High pressure spray leaks can easily catch fire. Any spray finishing using flammable or combustible liquids must meet the requirements of OSHA 29 CFR 1910.106 and NFPA 33 3 EMERGENCY PLANS AND PROCEDURES Every employee needs to know the emergency procedures to be used in the event of combustible metal fires or explosions at the die casting plant. Basic issues are the ability to evacuate and/or to actively respond to emergencies. Emergency Response A careful assessment (“size-up”) of the situation is important to anyone attempting to act on or suppress a combustible metal fire. This is an important question. “Can the fire be isolated and safely allowed to burn out?” Small and incipient fires may be contained using Class D extinguishing agents. Large fires can be difficult, even impossible to extinguish. They must be allowed to burn out. Only an organized, trained and properly equipped fire brigade or department should attempt to respond to a large combustible metal fire. All others must evacuate the area. Knowledge and familiarity with the products involved are critical to safety. The state of the material and the quantities involved (or potentially involved) are keys to the type response, e.g.: chips, fines, dust, light or heavy castings, ingots; Remember – dusts and fines have the potential to explode if airborne in the presence of an ignition source. If a fire is burning in a collector or other closed container, the potential for an explosion must be considered. A fire involving a large amount of product can be dangerous, especially within a building. Responders need to know that extreme caution is necessary. Heat and smoke can build up more rapidly than fires in ordinary combustibles. Large fires are often impossible to extinguish and must be allowed to burn out. Isolate the burning material as much as possible if this can be done safely. Water in contact with molten metal will cause hydrogen explosions and throw material about. Water may be used with care on products and exposures that are not involved in the fire. Appropriate drainage must be available to prevent water from contacting burning material. If the fire has been extinguished, the temperature of burned products must be allowed to cool. A “flare-up” may occur if the burned material is disturbed prior to complete oxidation and self extinguishment. Emergency Preparedness A comprehensive emergency preparedness program is necessary wherever combustible metals are processed, handled, used or stored. Safety experts have identified the need for a plan including specific actions to take in the event of a combustible metals fire and coordination 4 of the plan between plant management and everyone who will be responding to an emergency. OSHA regulations related to emergency plans are listed at 29 CFR 1910.38 & 1910.120. All employees in areas where combustible metals are handled need training regarding the following: The hazards of their working area; What they need to do in case of fire or explosion; The location and operation of: • Electrical switches and alarms; • First-aid equipment; • Safety equipment; and, • Fire extinguishing equipment. Permissible ways of fighting incipient combustible metal fires and for isolating fires; Hazards of causing dust clouds; The dangers of applying liquids to incipient metal fires; Safe and proper evacuation of the work area; Equipment operation, start-up, shut-down and how to respond to upsets; Need for and function of relevant fire and explosion protection systems; and, Details of the emergency response plan. CLOTHING FIRES Special flame retardant, antistatic clothing should be used for dusty jobs. Molten metal jobs also create the need for suitable heat resistant clothing and equipment. A major concern is that every employee must know what to do in the event his or her clothing starts on fire.