Flammable Materials

Recognizing Flammability Hazards in the Laboratory

Chemical structures which should serve as a warning sign

Using chemical labels as an aid

As an aid in identifying the chemicals which pose a flammability hazard in the laboratory, all chemical manufacturers are required to include relevant information on the chemical label. One of the most common grading systems is that developed by the National Fire Protection Association (NFPA). In this system, chemicals are rated from 0 (non-flammable) to 4 (extremely flammable). It is important for all laboratory personnel to recognize and become familiar with the NFPA diamond and understand the grading levels established by the NFPA for flammable materials. The red portion of the diamond gives an indication of the flammability of the material.

NFPA System for Flammability Rating

Rating     Hazard Description

  0	Materials that will not burn.
			
  1	Materials that must be preheated before they will ignite.

  2	Materials that must be moderately heated or exposed to 
  	relatively high ambient temperatures before they will ignite.

  3	Liquids and solids that can ignite under almost all 
  	temperature conditions.

  4	Materials which will rapidly vaporize at atmospheric 
  	pressure and normal temperatures, or are readily dispersed in 
  	air and which burn readily.

Another warning that indicates that a material is flammable is the presence of the flame on the chemical label. This is a standard symbol required by the Department of Transportation (DOT) to be used on all packages offered for transport over public highways, airways or by sea, which carry materials classified as an ignition hazard.

It is important that all lab personnel are familiar with these symbols that are associated with flammable materials. Always look for these warnings! Never handle a potentially flammable chemical until you are aware of the hazards, the level of protection required to work safely with the material, and the appropriate response should an accidental release occur. In addition to alerting the user about flammability hazards, many manufacturers use the label to list storage and use conditions that, if followed, will reduce the hazard involved.

Classes of Flammable Materials

Any substance that can burn is considered combustible. This includes common materials found in the lab which are not often thought of as a hazard, such as paper towels, stacks of journals and notebooks, as well as chemicals that are stored. Efforts must be exerted to avoid situations where these items might become involved in or contribute to a fire.

Though you must keep in mind the hazards posed by combustible materials, the real threat of fire lies with flammable materials. These are substances that are more likely to burn and will ignite more rapidly. Most flammable materials found in a laboratory setting will be in a liquid state, though there are numerous solids that must be used cautiously in areas where ignition sources exist.

The Department of Transportation (DOT) is responsible for determining what constitutes a flammable material, and has offered the following definitions for ignitable materials:

Combustible Liquid: Any liquid having a flash point above 100F and below 200F
Flammable Liquid: Any liquid having a flash point below 100F
Flammable Gas: A compressed gas that satisfies the criteria for flame projection, lower flammability limit and flammability range
Flammable Solid: A non-explosive material that is capable of producing fire as a result of friction, heat retained from production or which, if ignited, produces a serious transportation hazard.

These definitions are based on the flammabilty characteristics of the material, specifically the flash point.

FLASH POINT is the minimum temperature at which a
liquid gives off vapor in sufficient concentrations to
allow the substance to ignite.

The NFPA, has further broken flammable and combustible materials into storage categories based on the flash point of the material. The result is that ignitable materials are subdivided into three categories of flammable materials and two categories of combustible materials.

Classification	Term	Flash Point and Boiling Point	Examples
Class IA	Flammable	Below 73F Boils below 100F	ethyl ether, acetaldehdye, methyl formate, pentane
Class IB	Flammable	Below 73F Boils above 100F	acetone, benzene, carbon disulfide, ethanol, toluene
Class IC	Flammable	Above 73F Boils below 100F	xylene, butyl alcohol, amyl acetate
Class II	Combustible	At or above 100F	glacial acetic acid, formaldehyde, hydrazine
Class IIIA	Combustible	At or above 140F	naphthalene, octyl alcohol
Class IIIB	Combustible	At or above 200F	glycerine, propylene glycol

The flashpoint provides the user with information about how flammable a material is. Many of the common organic solvents and chemicals used in the laboratory have flash points well below room temperature. What this means, that at or above that temperature there exists sufficient vapor, in correct concentration, to ignite if an ignition source is provided. Though the flashpoint provides a baseline for danger, other conditions may exist which would lower the flashpoint below the accepted value. Some of these conditions include:

situations that produce mists
environments which are oxygen-rich
increasing system pressure

Safe Handling of Flammable Liquids

Storage of flammable materials

Know the limits!
The NFPA has established guidelines for the quantity of flammable materials that may be stored safely in various use and storage situations. The limits for laboratories are as follows:

Storage Container or Situation	Quantity Allowed
glass bottles (i.e., not in safety cans), out on bench or shelves	10 gallons, all classifications combined
in approved safety cans	25 gallons, all classifications combined
in approved safety cabinets	60 gallons, all classifications combined

Recognize the hazard
Know what kind of material you are working with and the hazards associated with it. Some of this information is contained on the chemical label and quite a bit more on the MSDS. Know that certain classes of chemicals are more hazardous because of their structure, instability or environment. These materials are flammable but they are also categorized as reactives.
Isolate the hazard
Confine the material

Ventilate the area
The greatest hazard associated with flammable materials is the creation of a "flammable atmosphere" by high concentrations of flammable vapors. The potential of a flammable atmosphere increases as the environment temperature increases in areas where flammables are stored or are in use. As the temperature rises, the production of vapors at the surface of the flammable material is enhanced, thus increasing the vapor concentration in poorly ventilated areas. Each flammable substance has a corresponding "flammable range" at which concentrations a fire may result if an ignition source is at hand. The flammability range consists of an upper and lower concentration boundry that indicates where the danger lies -- between the 2 limits. Examples of flammability ranges for common laboratory chemicals are shown in the following table.

Chemical	Class	Flammability Limit (percent volume in air)
Chemical	Class	Lower	Upper
acetaldehyde	IA	4.0	60.0
acetone	IB	2.6	12.8
benzene	IB	1.3	7.1
carbon disulfide	IB	1.3	50.0
cyclohexane	IB	1.3	8.0
ether	IA	1.9	36.0
ethanol	IB	3.3	19.0
hexane	IB	1.1	7.5
methanol	IB	6.7	36.0
methyl ethyl ketone	IB	1.8	10.0
pentane	IA	1.5	7.8
toluene	IB	1.2	7.1

What's important to note about the flammability range is that some chemicals have a very wide range of flammability (see for instance, acetaldehyde, carbon disulfide, ether and methanol). As you might expect, these chemicals are particularly hazardous because the window for ignition is much wider --increased vigilance must be exercised when using these materials!

Explosion proof equipment as required
Eliminate ignition sources

Risk management

Education
The single most effective tool in fighting fires in the laboratory is EDUCATION! All lab personnel should be required to attend a safety presentation that addresses the hazards assocaited with working with flammable materials. Part of this education should include hands-on use of at least one type of fire extinguisher (dry powder, ABC), and preferably also CO₂. Other topics should include safe storage of flammables, emergency response, recognizing ignition sources, disposal of waste flammables, and health issues associated with solvent use.

Recognizing ignition hazards

Fires don't just happen. Three key ingredients are required for ignition to occur. Each of these three ingredients make up the three legs of what is known as the "fire triangle". Fuel is one ingredient, and in the laboratory setting, the biggest, and most dangerous, fuel source is the stockpiles of flammable chemicals used daily. The second requirement is oxygen. Fires cannot burn without an oxygen source. This can be in the form of air, chemical oxidizers, or cylinders of oxygen. For the ignition to occur, the fuel and air must come in contact. But mixtures of these two ingredients do not necessarily lead to a fire situation; there must also be enough energy to break and reform the chemical bonds. The final leg of the fire triangle supplies the necessary energy, or spark, that ignites the fuel/air mixture. With the triangle completed, a fire is likely.

It is important to recognize what constitutes an ignition hazard. Many fires occur because people are unaware of what is a hazard, or are careless when working with flammables around potential ignition sources. Examples of ignition sources are:

cigarettes
open flames from matches, busen burners, pilot lights
friction or grinding
static electricity
sparks generated when lights or motors switch on (especially common fire hazard for domestic refigerators where flammables are stored)
hot plates and heating ovens
exposure of pyrophoric materials to air, or water reactive materials to moisture
LASER beam

And don't forget about the vapors given off from an open container of volatile liquid! Many fires have occured when the vapors from an open container traveled along the lab bench to an ignition source and were ignited.

Provide adequate fire protection

Personal protection

Safe Handling of Flammable Gases

NFPA sets limitations on the number of cylinders that should not be exceeded in a laboratory. Do not acquire more than:

three 10" x 50" flammable gas or oxygen cylinders and
three 4" x 15" cylinders of toxic gases (such as arsine, chlorine, fluorine, hydrogen cyanide, nitric oxide)
NFPA allows for the use of liquefied petroleum gas cylinders within the lab, however, Texas laws state that no liquefied petroleum gases (i.e., C₃ or C₄ such as butanes, propanes, etc.) may be kept within an occupied building (Texas Railroad Commission rules).

Created and maintained by Nancy Magnussen
last revised 2 Aug 1997
nancy@isc.tamu.edu