Laboratory Safety Manual - 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.

Title

Laboratory Safety Manual - Chapter 10: Fire Safety

Purpose

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.

Table of Contents

1. Introduction
2. Properties of Flammable and Combustible Substances
3. Sources of Ignition
4. Use of Flammable Substances
5. Storage Rules
6. Fire Extinguisher Labeling
7. Fire Extinguisher Maintenance
8. Training
9. Allowed Container Sizes for Flammable and Combustible Liquids

I. Introduction

Flammable substances are among the most common hazardous materials found in laboratories. The main objective in working safely with flammable liquids is to avoid accumulation of vapors and to control sources of ignition. However, the ability of a material to vaporize, ignite, or explode varies with the type or class of substance. Prevention of fires and explosions requires knowledge of the flammability characteristics (e.g. upper and lower flammability limits, ignition requirements, and burning rates) of materials encountered in the laboratory.

II. Properties of Flammable and Combustible Substances

A. Liquids

Flammable liquids have a flash point below 100°F (37.7°C) and a vapor pressure that does not exceed 40 psi (276 kPa). By contrast, combustible liquids have a flash point at, or above, 100°F (37.7°C). Classes of flammable and combustible liquids are further defined in Appendix 10-A.

The flash point is the lowest temperature, determined by standard tests, at which a liquid gives off vapor in a sufficient concentration to form an ignitable mixture with air near the liquid's surface within the test vessel. Many common laboratory solvents and chemicals have flash points that are lower than room temperature.

It is the vapor, not the liquid, that burns. The rate at which different liquids produce flammable vapors depends on their vapor pressure. The degree of fire hazard also depends on their ability to form combustible or explosive mixtures with air.

B. Solids

The United States Department of Transportation (DOT) defines and classifies flammable solids in one of three categories (source: 49 CFR 173.124):

1. 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.
2. Class 4, Division 4.2: Spontaneously Combustible Material–
   Pyrophoric (air-reactive) materials or self-heating materials, which are likely to self-heat when in contact with air, even without an energy supply.
3. 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 often found on the substance container as well.

Figure 10.1. DOT placards for Class 4 materials. Images shown left to right; Class 4, Division 4.1: Flammable Solid; Class 4, Division 4.2: Spontaneously Combustible Material; and Class 4, Division 4.3: Dangerous When Wet Material. 

C. Gases

The DOT defines flammable gases in 49 CFR 173.115 as materials that are:

• 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.

D. Ignitability

The auto-ignition temperature of a substance, whether solid, liquid or gaseous, is the minimum temperature required to initiate self-sustained combustion independent of a heat source.  For example, a steam line or a glowing light bulb may ignite carbon disulfide (ignition temperature 80°C [176°F]). Diethyl ether (ignition temperature 160°C [320°F]) can be ignited by the surface of a hot plate. Silane gas (ignition temperature 21°C [69.8°F]) can spontaneously ignite at or near room temperature.

Spontaneous ignition or combustion occurs when a substance reaches its ignition temperature without the application of external heat. The possibility of spontaneous combustion should be considered, especially when storing and disposing of materials. 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), alkali metals (lithium, sodium, potassium, rubidium, and cesium), finely divided metal powders, and phosphorus.

III. Sources of Ignition

Many potential sources of spark, flame, or heat in laboratories can ignite flammable substances, such as open flames, static electricity, lighted matches, and hot surfaces. When flammable materials are in use, pay close attention to all potential ignition sources in the vicinity. The vapors of flammable liquids are heavier than air, and can travel considerable distances. Be aware of this possibility and take special note of ignition sources positioned at lower levels than the level of the flammable liquid in use.

Flammable vapors from substantial sources, such as spills, can descend into stairwells and elevator shafts and ignite on a lower floor. If the vapor path is continuous, the flame can propagate back from the point of ignition 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, bonding could be made to the liquid rather than the container.

IV. Use of Flammable Substances

The basic precautions for safe handling of flammable materials include the following:

• 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 transferring flammable liquids using metal equipment, prevent static-generated sparks by bonding and using ground straps.
• Ventilation is one of the most effective ways to prevent the formation of flammable mixtures. Use a fume hood when handling appreciable quantities of flammable substances (e.g. transferring between containers or working with an open container, especially if 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 must not be drawn from or filled inside buildings without provisions to prevent the accumulation of flammable vapors in hazardous concentrations.

V. Storage Rules

Basic rules for safe storage of flammable materials include the following:

• 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 made by manufacturers of flammable and combustible liquids generally meet these specifications.
• Flammables stored in the openly 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 currently planned, as future research needs may involve flammable materials. Existing domestic refrigerators in labs must have a sign (similar to Figure 10.2) stating that no flammable storage is permitted.
• “Safety” refrigerators (Figure 10.3) are recommended for laboratories as they have electrical contacts (door switch, light, thermostat, etc.) removed or exteriorized.
• “Explosion-proof” refrigerators (Figure 10.4) are generally not necessary except in unusual circumstances, such as inside a storage room (for flammables) or other potentially hazardous atmospheres. Note that each refrigerator is clearly labeled if it is for flammable material storage or explosion-proof use.
• Flammable liquids must not block laboratory aisles or exits. Do not place flammable storage cabinets near an exits or in hallways.
• Keep flammable liquids away from heat and direct sunlight.
• Store flammable liquids in a manner 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.
• The maximum allowable size of containers for flammable and combustible liquids must be in accordance with Section IX: Allowed Container Sizes for Flammable and Combustible Liquids.
• 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 used for storage. The maximum quantities allowed per laboratory unit is as follows:
  1. Shelf or open storage/use
     1. Glass, approved plastic, or metal containers: 10 gallons (37.9 liters)
     2. Safety cans: 25 gallons (94.7 liters)
  2. Approved storage cabinets
     1. Class I liquids: 30 gallons (113.6 liters)
     2. Class I, II, & III liquids combined: 60 gallons (227.2 liters)
  3. Inside storage room (meeting NFPA Code recommendations)
     1. With sprinkler: 4 -10 gal per ft²
     2. Without sprinkler: 2 - 4 gal per ft²
  4. For laboratories located on upper floors of 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.

Figure 10.2. Example signage for lab refrigerators designated for non-flammable material storage (available on the EHS website).

Figure 10.3. Example of a "safety refrigerator" or refrigerator that can store flammable materials.

Figure 10.4. Example of explosion-proof refrigerator from LABRepCo.

VI. Fire Extinguisher Labeling

For ease of identification, labels A, B, C, D, and K (as well as more recently introduced pictograms) indicate the type of fire an extinguisher can be used on.

Most chemical laboratory fire hazards require multipurpose dry chemical extinguishers (ABC) located in hallways. “Gas” extinguishers containing carbon dioxide (CO2) provide 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 permitted for use on campus. If your lab has one, please contact EHS (919-962-5507) so that it can be replaced.

VII. Fire Extinguisher Maintenance

EHS personnel perform annual inspection and maintenance of campus fire extinguishers. Laboratory personnel are encouraged to check their extinguishers regularly for these items:

• Accessibility
• 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

VIII. Training

EHS offers training in the proper use of fire extinguishers and building evacuation. For information and training dates, contact EHS at 919-962-5507. You are NOT required to use a fire extinguisher on campus. However, if you choose to use one on campus you must receive training in its correct use.

Additional information on University Fire Safety policies can be found in Chapter 4.

IX. Allowed Container Sizes for Flammable and Combustible Liquids

Flammable Liquids

• 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).

Combustible Liquids

• 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, with a capacity of no more than 5-gallons capacity, featuring a spring-closing lid and spout cover, and designed to safely relieve internal pressure when subjected to fire exposure.

Figure 10.5. Example photo of safety cans.

Many types of containers are required depending on the quantities and classes of flammable or combustible liquids in use.

NFPA 30 Chapter 9 Table 9.4.3

NFPA 30 Chapter 9.4.3.2

Class IA and Class IB liquids shall be permitted to be stored in glass containers with a capacity of not more than 1.3 gal (5 L)  if the required liquid purity (such as American Chemical Society analytical reagent grade or higher) would be compromised by storage in metal containers, or if the liquid can cause excessive corrosion of a metal container.

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