Chapter 10: Fire Safety
This chapter outlines the properties of flammable liquids, solids, and gases, the proper storage and use of flammable substances, and the properties of fire extinguishers.
The flash point is the lowest temperature, as determined by standard tests, at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air near the surface of the liquid within the test vessel. Many common laboratory solvents and chemicals have flash points that are lower than room temperature.
Actually, the vapor, not the liquid, burns. The rate at which different liquids produce flammable vapors depends on their vapor pressure. The degree of fire hazard depends also on the ability to form combustible or explosive mixtures with air.
- Class 4, Division 4.1: Flammable Solid–
Self-reactive materials that are thermally unstable and can undergo a strongly exothermic decomposition even without participation of oxygen; desensitized explosives also fall within this category.
- Class 4, Division 4.2: Spontaneously Combustible Material–
Pyrophoric (air-reactive) materials or self-heating materials, likely to self-heat when in contact with air and without energy supply.
- Class 4, Division 4.3: Dangerous when wet material–
Liable to spontaneously combust or give off flammable/toxic gas when in contact with water.
Flammable, pyrophoric, self-heating, or dangerous when wet solids will have the following DOT placards on the shipping container when transporting more than 1,001 pounds of Division 4.1 or 4.2 materials, or any quantity of Division 4.3 material. Smaller versions of these placard labels are frequently on the substance container as well.
- Gases at 20° C (68° F) or less and 101.3 kPa (14.7 psi) of pressure, and:
- Are ignitable at 101.3 kPa (14.7 psi) when in a mixture of 13 percent or less by volume with air; or
- Have a flammable range at 101.3 kPa (14.7 psi) with air of at least 12 percent regardless of the lower limit.
The DOT classifies flammable gases as Class 2, Division 2.1 materials.
Spontaneous ignition or combustion takes place when a substance reaches its ignition temperature without the application of external heat. Consider the possibility of spontaneous combustion, especially when materials are stored or disposed. Materials susceptible to spontaneous combustion include oily rags, dust accumulation, organic materials mixed with strong oxidizing agents (such as nitric acid, chlorates, permanganates, peroxides and persulfates), the alkali metals (lithium, sodium, potassium, rubidium, and cesium), finely divided metal powders, and phosphorus.
Flammable vapors from substantial sources such as spills can descend into stairwells and elevator shafts and ignite on a lower story. If the path of vapor is continuous, the flame can propagate itself from the point of ignition back to its source.
Properly bond and ground all metal lines and vessels dispensing flammable substances to discharge static electricity. When nonmetallic containers (especially plastic) are used, the bonding can be made to the liquid rather than to the container.
- Handle flammable substances only in areas free of ignition sources.
- Do not heat flammable substances with an open flame. Preferred heat sources include steam baths, water baths, oil baths, heating mantles and hot air baths.
- When you transfer flammable liquids in metal equipment, avoid static-generated sparks by bonding, and the use of ground straps.
- Ventilation is one of the most effective ways to prevent the formation of flammable mixtures. Use an exhaust hood when you handle appreciable quantities of flammable substances (e.g. transferring between containers or in an open container, especially if you are heating it).
- When withdrawing a flammable liquid from a drum, or filling a drum, both the drum and other equipment must be individually, electrically grounded and bonded to each other.
- Containers of flammable liquids shall not be drawn from or filled within buildings without provisions to prevent the accumulation of flammable vapors in hazardous concentrations.
- Store flammable and combustible liquids only in approved containers. Approval for containers is based on specifications developed by organizations such as DOT, the Occupational Safety and Health Administration (OSHA), the National Fire Protection Association (NFPA), or the American National Standards Institute (ANSI). Containers used by the manufacturers of flammable and combustible liquids generally meet these specifications.
- Flammables stored in the open in the laboratory work area shall be kept to the minimum necessary for the work being done.
- Do not store flammable liquids in domestic type refrigerators. Domestic type refrigerators are not recommended for laboratory use, even if flammable storage is not contemplated, since future research needs may require the use of flammables. Existing domestic refrigerators in labs must have a posting (similar to Figure 10.2) stating that no flammable storage is permitted. “Safety” refrigerators (Figure 10.3) are recommended for laboratories. These have the electrical contacts (door switch, light, thermostat, etc.) removed or exteriorized. “Explosion-proof” refrigerators (Figure 10.4) are not necessary except in unusual circumstances, such as within an inside storage room (for flammables) or other potentially hazardous atmospheres. Note that each of these is clearly labeled if it is for flammable material storage or explosion-proof.
- Flammable liquids must not block laboratory aisles or exits. Do not locate flammable storage cabinets near an exit or in the hallway.
- Keep flammable liquids away from heat and direct sunlight.
- Store flammable liquids in a way that prevents accidental contact with strong oxidizing agents (such as permanganates or chlorates).
- University policy prohibits smoking in all University buildings; remove other sources of ignition from areas where flammable liquids are stored.
- Maximum allowable size of containers for flammable and combustible liquids shall be in accordance with Appendix 10-A.
- The potential fire hazard also depends on the total quantity of flammable and combustible liquids present within a laboratory unit (room) and the type of containers in which the liquids are stored. The maximum quantity allowed per laboratory unit is as follows:
- Shelf or open storage/use
- glass, approved plastic or metal: 10 gallons (37.9 liters)
- safety cans: 25 gallons (94.7 liters)
- Approved storage cabinets
- Class I: 30 gallons (113.6 liters)
- Class I, II, & III: 60 gallons (227.2 liters)
- Inside storage room (meeting NFPA Code recommendations)
- with sprinkler: 4-10 gal/ft2
- without sprinkler: 2-4 gal/ft2
- For laboratories located on upper floors within new or remodeled buildings, the limits for flammable and combustible liquids might be more restrictive due to the North Carolina Fire Prevention Code. Refer to Chapter 4 for more details, or contact EHS at 919-962-5507 if you have questions.
- Shelf or open storage/use
|A||Ordinary Combustibles||Fires in paper, cloth, wood, rubber, and many plastics require a water or dry chemical type extinguisher labeled A.|
|B||Flammable Liquids||Fires in solvents and other flammable liquids require dry chemical, Halon™, or CO² extinguisher labeled B.|
|C||Electrical Equipment||Fires in wiring, fuse boxes, energized equipment and other electrical sources require a dry chemical, Halon™, or CO² extinguisher labeled C.|
|D||Metals||Combustible metals such as magnesium and sodium require special extinguishers labeled D.|
|K||Cooking Oils and Fats||Wet chemical extinguishers specially designed to put out fires of cooking oils or fats are labeled K; unlikely to be needed in a laboratory setting.|
Most chemical laboratory fire hazards require multipurpose dry chemical extinguishers (ABC) located in hallways. “Gas” extinguishers containing carbon dioxide (CO2) offer a first defense against flammable liquids or electrical fires without leaving a powder residue that could harm electronic equipment. Halon™ 1211 fire extinguishers are no longer to be used on campus. If your lab has one, contact EHS so that it can be replaced.
- Charge Gauge (CO2 units lack gauges)*
- Tamper Seal
- Physical Damage
Report any problems or missing extinguishers to EHS at 919-962-5507.
*EHS recharges extinguishers at no cost to the department or building to which the extinguisher was assigned if one the following applies:
- If there is evidence of pressure leakage, or
- If the extinguisher has been used
Additional information on University Fire Safety policies is found in Chapter 3 of the UNC Environment, Health and Safety Manual.
- Class IA:
- Liquids having flash points below 73°F (22.8°C) and having a boiling point below 100°F (37.8°C).
- Class IB:
- Liquids having flash points below 73°F (22.8°C) and having a boiling point at or above 100°F (37.8°C).
- Class IC:
- Liquids having a flash point at or above 73°F (22.8°C) and below 100°F (37.8°C).
- Class II:
- Liquids with flash points at or above 100°F (37.8°C) and below 140°F (60°C).
- Class III:
- Liquids with flash points at or above 140°F (60°C).
- Safety Can:
- An approved container, of not more than 5-gallons capacity, having a spring-closing lid and spout cover and so designed that it will safely relieve internal pressure when subjected to fire exposure.
Many types of containers are required depending on the quantities and classes of flammable or combustible liquids in use.
|Class IA||Class IB||Class IC||Class II||Class III|