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SECTION 7: Safe Work Practices and Procedures
7B: Flammable Materials
Properties
of Flammable and Combustible Liquids
Flammable and combustible liquids vaporize and form flammable mixtures with
air when in open containers, when leaks occur, or when heated. To control
these potential hazards, several properties of these materials, such as
volatility, flashpoint, flammable range and autoignition temperatures must
be understood. An explanation of these terms and other properties of flammable
liquids is available the Laboratory
Training Guide. Information on the properties of a specific liquid
can be found in that liquid’s material
safety data sheet (MSDS), or other reference material.
Storage of
Flammable and Combustible Liquids
Flammable and combustible liquids should be stored only in approved containers.
Approval for containers is based on specifications developed by organizations
such as the US Department of Transportation
(DOT), OSHA, the National
Fire Protection Agency (NFPA) or American
National Standards Institute (ANSI). Containers used by the manufacturers
of flammable and combustible liquids generally meet these specifications.
Safety
Cans and Closed Containers
 Many types of containers
are required depending on the quantities and classes of flammable or combustible
liquids in use. A safety can is
an approved container of not more than 5 gallons capacity that has a spring
closing lid and spout cover. Safety cans are designed to safely relieve
internal pressure when exposed to fire conditions. A closed
container is one sealed by a lid or other device so that
liquid and vapor cannot escape at ordinary temperatures.
Flammable
Liquid Storage Cabinets
A flammable liquid storage cabinet
is an approved cabinet that has been designed and constructed to protect
the contents from external fires. Storage cabinets are usually equipped
with vents, which are plugged by the cabinet manufacturer. Since venting
is not required by any code or the by local municipalities and since venting
may actually prevent the cabinet from protecting its contents, vents should
remain plugged at all times. Storage cabinets must also be conspicuously
labeled "FLAMMABLE – KEEP FIRE AWAY".
Refrigerators
Use only those refrigerators that have been designed and manufactured for
flammable liquid storage. Standard household refrigerators must not be used
for flammable storage because internal parts could spark and ignite. Refrigerators
must be prominently labeled as to whether or not they are suitable for flammable
liquid storage.
Storage
Considerations:
- Quantities should be limited to the amount necessary for the work
in progress.
- No more than 10 gallons of flammable and combustible liquids,
combined, should be stored outside of a flammable storage cabinet
unless safety
cans are used. When safety cans are used, up to 25 gallons may
be stored without using a flammable storage cabinet.
- Storage of flammable liquids must not obstruct any exit.
- Flammable liquids should be stored separately from strong oxidizers,
shielded from direct sunlight, and away from heat sources. See Anecdotes for
a description of an incident involving a flammable material stored
near a hot plate.
Handling Precautions (top)
The main objective in working safely with flammable liquids is to avoid
accumulation of vapors and to control sources of ignition.
Besides the more obvious ignition sources, such as open flames from Bunsen
burners, matches and cigarette smoking, less obvious sources, such as
electrical equipment, static electricity and gas-fired heating devices
should be considered. Accounts of a few of the fires that have occurred
in our laboratories may be found in Anecdotes.
Some electrical equipment, including switches, stirrers, motors, and
relays can produce sparks that can ignite vapors. Although some newer
equipment have spark-free induction motors, the on-off switches and speed
controls may be able to produce a spark when they are adjusted because
they have exposed contacts. One solution is to remove any switches located
on the device and insert a switch on the cord near the plug end.
Pouring flammable liquids can generate static electricity. The development
of static electricity is related to the humidity levels in the area. Cold,
dry atmospheres are more likely to facilitate static electricity. Bonding
or using ground straps for metallic or non-metallic containers can prevent
static generation.
- Control all ignition sources in areas where flammable liquids
are used. Smoking, open flames and spark producing equipment should
not
be used.
- Whenever possible use plastic or metal containers or safety cans.
- When working with open containers, use a laboratory
fume hood to control the accumulation of flammable vapor.
- Use bottle carriers for transporting glass containers.
- Use equipment with spark-free, intrinsically safe induction motors
or air motors to avoid producing sparks. These motors must meet National
Electric Safety Code (US DOC, 1993) Class 1, Division 2, Group C-D
explosion
resistance specifications. Many stirrers, Variacs, outlet strips,
ovens, heat tape, hot plates and heat guns do not conform
to these code requirements.
- Avoid using equipment with series-wound motors, since they are
likely to produce sparks.
- Do not heat flammable liquids with an open flame. Steam baths,
salt and sand baths, oil and wax baths, heating mantles and hot air
or nitrogen
baths are preferable.
- Minimize the production of vapors and the associated risk of ignition
by flashback. Vapors from flammable liquids are denser than air and
tend to sink to the floor level where they can spread over a large
area.
- Electrically bond metal containers when transferring flammable
liquids from one to another. Bonding can be direct, as a wire attached
to both
containers, or indirect, as through a common ground system.
- When grounding non-metallic containers, contact must be made directly
to the liquid, rather than to the container.
- In the rare circumstance that static cannot be avoided, proceed
slowly to give the charge time to disperse or conduct the procedure
in an inert
atmosphere.
Flammable Aerosols (top)
Flammable liquids in pressurized containers may rupture and aerosolize when
exposed to heat, creating a highly flammable vapor cloud. As with flammable
liquids, these should be stored in a flammable storage cabinet.
Flammable
and Combustible Solids
Flammable solids often encountered in the laboratory include alkali metals,
magnesium metal, metallic hydrides, some organometallic compounds, and sulfur.
Many flammable solids react with water and cannot be extinguished with conventional
dry chemical or carbon dioxide extinguishers. See Anecdotes for descriptions of incidents involving such materials.
- Ensure Class D extinguishers, e.g., Met-L-X, are available where
flammable solids are used or stored.
- Sand can usually be used to smother a fire involving flammable
solids. Keep a container of sand near the work area.
- If a flammable, water-reactive solid is spilled onto skin, brush
off as much as possible, then flush with copious amounts of water.
- NEVER use a carbon dioxide fire extinguisher for fires involving lithium
aluminum hydride (LAH). LAH reacts explosively with carbon
dioxide.
Catalyst Ignition
(top)
Some hydrogenated catalysts, such as palladium, platinum oxide, and Raney
nickel, when recovered from hydrogenation reactions, may become saturated
with hydrogen and present a fire or explosion hazard.
- Carefully filter the catalyst.
- Do not allow the filter cake to become dry.
- Place the funnel containing moist catalyst into a water bath immediately.
Purge gases, such as nitrogen or argon, may be used so that the catalyst
can be filtered and handled in an inert atmosphere.
 Section
7C: Peroxide Forming Compounds and Reactives
 Section
7A: General Considerations
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