Fire Prevention

Each year fire kills thousands of people and destroys billions of dollars worth of property.  These losses can be prevented.  Physical plant workshops, art classrooms, laboratories, theater scene shops, etc.─stocked with flammable and combustible liquids, gases, and solids─contain all the elements of a potential fire. 

The Fire Triangle

For a fire to start, three conditions must be met at the same time.

There must be something to burn─a fuel; a source of oxygen (an oxidizer); but most importantly, there needs to be an initiating event that imparts sufficient energy to start a chain reaction─an ignition source.  These three necessary factors are each at the corners of an equilateral triangle, the fire triangle, whose overlap is a chain reaction that results in the rapid oxidation of a fuel─fire.

A fire will not always start when the three legs of the fire triangle meet, unless all three elements are present in the required amounts. For instance, vapors from a flammable liquid must be mixed with a certain amount of air in order to ignite and propagate a flame.

The Flammable Range

Flammable vapors and gases will burn only if their concentration in air is within a certain range (called the flammable range).  The lowest concentration at which a fuel/air mixture will burn is called the Lower Flammable Limit (LFL); below this there is too little fuel (the mixture is too lean).  The highest concentration at which a fuel/air mixture will burn is the Upper Flammable Limit (UFL); above this there is not enough oxygen (the mixture is too rich).  Within this flammable range (sometimes also called the Lower and Upper Explosive Limits─LEL and UEL), there is enormous potential for fire or explosion.  For example, acetone will burn only when the vapor concentrations in air are between 2 ½ percent and 13 percent.

Adjustment of work habits is necessary to keep the vapor concentration too lean to burn─that is, well below the LFL.  Usually it is recommended to keep the vapor concentration below 25 percent of the LFL.

The Flash Point

A common measure of a liquid's ease of ignition is its flash point (the lowest temperature at which sufficient vapors form above the liquid to produce an ignitable mixture with air).  Solvents with flash points at or near room temperature are particularly hazardous because of the ease at which they catch fire when an ignition source is present.  Substitution of high flash point solvents for more dangerous low flash point solvents reduces the amount of flammable vapors produced and makes a fire less likely.  For example, mineral spirits (flash point over 100°F) is much safer than a similar naphtha product (flash point of 28°F).

For transportation regulation purposes, the U.S. Department of Transportation classifies all liquids with a flash point below 100°F as flammable and all liquids with flash points at or above 100°F as combustible.  For storage regulation purposes, the National Fire Protection Association (NFPA) has further subdivided flammable liquids into Classes IA, IB, and IC, and combustible liquids into Classes II, IIIA, and IIIB.

Normally, combustible liquids are not considered to be serious fire hazards at ambient temperatures.  However, heating a solvent to a temperature at or near its flash point will increase its fire hazard─causing a combustible liquid to act as if it were a flammable liquid.  This is because raising the temperature increases the amount of flammable vapor produced, thus contributing to the fuel leg of the fire triangle.  For instance, turpentine (whose flash point is 95°F) must be used with extra care at high ambient temperatures or in direct sunlight.

Vapor Pressure

A material's vapor pressure is a measure of its ability to evaporate.  The higher the vapor pressure, the higher the evaporation rate (and the lower the flash point), which results in more vapors being produced.  Consequently, liquids with high vapor pressures are greater fire hazards.  Substitution of a lower vapor pressure solvent, such as ethyl alcohol for the higher vapor pressure acetone, reduces both the amount of vapors and the risk of fire.

Auto-Ignition Temperature

Another measure of a material's ease of ignition is its auto-ignition temperature.  This is the temperature at which, in the presence of sufficient oxygen, a material will ignite on its own and burn (spontaneous ignition).  For example, carbon disulfide (with an extremely low auto-ignition temperature of 212°F) must be kept away from all heat sources.  Large amounts of highly flammable materials should be stored in a laboratory safe refrigerator (sometimes referred to as explosion-proof, although this designation is not quite correct).

Flammable Gases and Solids

The tall cylinder of acetylene welding gas that is a familiar sight in many physical plant facilities and art studio workshops should be stored and used properly according to the OSHA regulations.

Solids that burn include paper, wood, and cloth.  These pose a fire hazard mostly because they are not usually treated as potential fuels.  Solid materials (like rags or paper soaked with a flammable liquid) are quite dangerous due to the rapid evaporation of the flammable liquid from their surfaces.

Metals that burn (called pyrophoric) are an especially serious fire hazard, because it is very hard to put these fires out.  For the most part these materials are not frequently encountered on campus.

Storage & Handling

Since it is impossible to eliminate oxygen from the fire triangle, fire prevention depends on trying to eliminate sources of ignition and restricting the amount of flammable and combustible liquids.  Some simple rules that should always be followed to eliminate sources of ignition include:

Storage

Some of the major ways to reduce fire hazards in the storage of flammable and combustible liquids are:

  1. Choosing the least hazardous materials possible,

  2. Reducing the amounts stored to a minimum, and

  3. Using safe storage procedures and containers.

Labeling

Safe storage of flammable materials requires that the materials be adequately labeled as to their contents, fire hazards, and safe handling procedures.  Flammable liquids should carry the following label:

DANGER

FLAMMABLE

KEEP AWAY FROM HEAT, SPARKS & OPEN FLAMES

KEEP CLOSED WHEN NOT IN USE

Information pertinent to preventing and extinguishing fires is contained in Section V of the product's Material Safety Data Sheet (MSDS).  This section contains the material's flash point and flammability range, as well as the proper fire fighting equipment to use in the event of a fire.  This data, and the information about the product's physical properties contained in Section IV, are valuable for proper labeling, comparing various products flammability range, and choosing less hazardous materials.

Another method of labeling is the NFPA 704 System of Hazard Identification.  This is a symbol hazard system intended for use on fixed locations, such as laboratory entrances, storage rooms, etc.  It tells a firefighter or other person of the hazards in the area.  This NFPA system uses the NFPA diamond as the symbol.  The numbers 0 through 4 are placed in the three upper quadrants of the diamond.  These represent the degree of hazard for health hazard, flammability, and reactivity.  The number 0 indicates the least degree of hazard, and 4 the highest.  The bottom quadrant is often used for the radiation hazard symbol or water reactivity (a letter W with a bar through it).

Storage Amounts

Local and state fire codes limit the amounts of flammable and combustible liquids that can be stored in various locations.  Check with your local fire department.

Storage Areas

The best location to store large amounts of flammable and combustible liquids is in a separate outside building.  If this is not possible, then a suitable flammable storage cabinet or inside storage room should be built.  NFPA 30 (Flammable & Combustible Liquids Code) describes the requirements for inside storage rooms.  These can include walls, floors and ceiling with a fire resistance rating of 2 hours, class B fire doors, automatic fire protection systems, and mechanical ventilation─depending on the amount stored.  If flammable liquids (Class I) are stored in this room, then explosion vents, and Class I-Division 2 electrical wiring and fixtures are required.  Only flammable and combustible liquids should be stored in these rooms.

Storage Containers

All containers of flammable and combustible liquids must be stored in accordance with established safety procedures that isolate incompatible materials from each other. In addition, the amounts stored should be kept to a minimum to reduce the risk of fire.  Note that in instructional laboratories, the largest container size permitted for flammable liquids is 1 gallon (or a 2 gallon safety can).

Portable Safety Cans

Quantities of flammable liquids exceeding one pint should be stored in safety cans that are approved or listed by recognized testing laboratories, e.g., Factory Mutual or Underwriters Laboratories.  These have self-closing covers, flame arrestor screens, and pressure release devices.  Similar containers are used for storage of waste solvents.

Drums

Liquids often come in 5 gallon and 55 gallon drums. The maximum size of drum that should be stored is 5 gallons; 55 gallon drums should only be stored in a separate storage area away from heat and sunlight.

Flammable Storage Cabinets

If the amounts of flammable and combustible liquids present are too small to warrant a separate storage room, they should be stored in a flammable storage cabinet that has been built to meet OSHA and NFPA standards.  Cabinets should be labeled in large letters: FLAMMABLE KEEP FIRE AWAY.

Flammable storage cabinets do not need to be vented unless required by local codes.  A maximum of 120 gallons of Class I, II and IIIA liquids may be stored in a flammable storage cabinet; of this total, not more than 60 gallons may be of Classes I and II.  A maximum of not more than three such cabinets may be located in a given fire area (an area of a building separated from the rest of the building by construction having a fire resistance rating of at least one hour).

Dispensing

Many fires are started by the improper dispensing of flammable liquids.  The pouring and mixing of flammable materials should be restricted to a special well-ventilated area.  When dispensing from drums, use approved transfer pumps or drum faucets.  When pouring flammable liquids from a drum to a metal container (e.g., a safety can), ground the drum and bond the metal container to the drum to prevent the build-up of any static charge.  This bonding is done with a braided wire with large metal clips to connect the drum and container, and a grounding line from the drum to a ground.

Spills and Leaks

Flammable liquid spills can be reduced, and in some cases eliminated, by proper training and good housekeeping techniques. Should a spill occur, it must be quickly and safely cleaned up to prevent its flammable vapors from igniting.  A large quantity of absorbent (e.g., commercially available spill pillows) should be kept on hand in all areas used for storage, dispensing, or use of flammable liquids.

Once a spill has been collected onto the absorbent, it must be treated as a flammable material.  A metal container should be used to contain the absorbed flammable material, and disposed of separately from the regular trash─preferably wrapped in a separate plastic bag.

Large spills of flammable liquids (more than a quart) are especially dangerous and need special cleanup procedures.

Fire Fighting

If you do not succeed in preventing a fire, then you have to extinguish it.  The timely use of the proper fire extinguisher will slow a fire and give professional fire fighters time to arrive.  There is a wide variety of fire extinguishers─each designed to fight a particular type of fire. The use of the wrong fire extinguisher will prove ineffective on a fire, and may even spread the fire.

Fire Extinguishers

Each class of fire has special fire extinguishers that are recommended for it.  Common types include the following:

Automatic Sprinkler Systems

Automatic sprinkler systems are commonly used in public buildings as a fire suppression method. There are several types, including water and halon.  This newsletter is just going to briefly discuss these types.

Water

The system of water pipes that sprays a mist when activated by the heat of a fire is common in older buildings.  Water sprinkler systems are, however, not common in museums and libraries for a variety of reasons.

Halon Systems

Halon automatic sprinkler systems spray a halogenated chemical─either Halon 1301 or 1211─onto the fire.  Halons, while effective fire retardants, decompose to toxic gases (such as hydrogen fluoride and hydrogen chloride) when heated. In addition, the halons themselves can be toxic at the high concentrations encountered in total flooding systems.  The use of halon deluge systems must be carefully planned, must only be used in enclosures, and never in conjunction with an automatic door closing mechanism that might trap workers or visitors.  See in particular the NFPA standards on halons.  Halon extinguishing systems are also quite expensive.

Procedures for Fire Fighting

OSHA has detailed regulations concerning firefighting procedures.  All employers must have a written fire prevention plan.  OSHA regulations allow for three situations:

  1. Total evacuation in case of fire alarm;

  2. Partial evacuation with some employees allowed to use fire extinguishers; and

  3. All employees allowed to use fire extinguishers.  If any employees are allowed to use fire extinguishers, then OSHA specifies training and other requirements.

Using Fire Extinguishers

If you are subject to use a fire extinguisher, the first step is to ask yourself whether or not you can effectively fight the fire at hand.  Small trash fires can be easily be put out; but when threatened with a large and fast moving fire, sound the alarm and wait for professional fire fighters to arrive.  An easy four-step plan will help in the event of a fire:

  1. If you think you can handle the fire, sound the fire alarm in order to set the emergency plan in operation.

  2. Grab the closest fire extinguisher that conforms to the type of fire. Remember, the wrong extinguisher will be ineffective, and can actually spread a fire.

  3. Activate the fire extinguisher and follow the directions for use.  (You should have had previous practice in using the fire extinguisher.)  Remember, even when the fire appears to be extinguished, it might not be.  Many smoldering fires are still hot enough to re-ignite.  Before you leave, make sure it is completely out.

  4. If at any time you feel overwhelmed, or the extinguisher charge runs out, leave the area and wait for the professional fire fighters to arrive.  Your guidance as to what type of fire and where it started will be quite valuable to them.   The actual procedures should be part of your fire prevention training, which should include actual practice in the use of fire extinguishers.

Maintenance

Fire fighting equipment must be well maintained and checked periodically for pressure and integrity─this can be inexpensively contracted out to an extinguisher service company.

The fire extinguishers must be placed prominently according to OSHA regulations (and not used for bookends, coat racks, or door stops).  A fire extinguisher cannot help in the event of a fire if nobody can find it or it does not work.  Other types of fire suppression equipment, such as sprinkler systems, must also meet the appropriate OSHA standard.

Remember!  Don’t cut corners when working with hazardous materials. Work safely by constantly remaining aware of the hazards of the materials you are working with.  Watch those storage areas where materials can accumulate.  This is one of the most common problems on our campuses throughout the state.