Here is What stipulates the flammability characteristics of laboratory solvents
A laboratory
houses several solvents which play diverse roles in analysis and synthesis
activities. The quantities of such solvents in laboratories are often much
lower than
those found in warehouses. Fortunately the fire hazards posed by
flammable solvents are less in laboratories in comparison to places of bulk
storage. The risk in laboratories is further reduced due to provision of
adequate ventilation, fume hoods and air- conditioning. However, fire hazards
in laboratories cannot be completely ruled out and tips on prevention of
laboratory fire accidents provides some suggestions on simonizing such
unfortunate incidents.
It becomes all
the more important for a laboratory worker to have a clear understanding of the
flammability characteristics that define combustible behaviour of such solvents
so that required precautions are taken during their handling and storage.
Flammable and
combustible characteristics of liquids
First of all
it is important to understand the dividing line between a flammable and
combustible liquid. Flammable liquids have the potential to ignite and catch
fire at normal laboratory temperatures whereas combustible liquids burn at
higher temperatures. In other words flammable liquids have flashpoints below
37.8^0C (100^0 F) whereas flashpoints of combustible liquids are above 37.8^0C
(100^0F) but below 93.3^0C (200^0F).
Flashpoint
This is the lowest temperature at
which a liquid produces sufficient vapour to ignite in presence of a source of
ignition. The entire liquid does not burn but the solvent vapour above the
liquid surface starts burning. The lower the flashpoint the higher is the fire
risk. Common laboratory solvents such as acetone, diethyl ether,toluene,etc
exhibit below ambient temperature flash points. An example is diethyl ether
which has high fire potential as its flashpoint is – 45^0C which is far below
ambient temperature of a laboratory.
Auto ignition
point
A liquid can
auto ignite itself when it is heated. The liquid catches fire on reaching
the auto ignition temperature even in the absence of a source of ignition.
Fortunately auto ignition temperatures of common solvents are high (400 to
500^0C) than laboratory ambient temperatures but it is advisable to keep such
solvents away from hot plates and other heat generating equipments.
Flammable and
explosive limits
Flammable limits
define the concentration limits of solvent vapour in air that can lead to
burning or explosion in presence of a flame or any other source of ignition.
Lower
explosive limit (LEL) is the lowest vapour concentration that will burn or
explode if ignited. In other words the air- fuel mixture is lean on fuel for
ignition
Upper
explosive limit (UEL) is the highest vapour concentration that will burn or
explode if ignited. Above this concentration the mixture is too fuel rich to
support combustion
It can be inferred
that the solvent – air mixture can be ignited only between the lower and upper
explosive limits
On the basis
of Flash point the National Fire Protection Association (NFPA) has classified
solvents into different classes based on their fire hazard potential. NFPA 30
code classifies such solvents according to their fire hazard potential.
You should
keep in mind that fires resulting from flammable and combustible liquids spread
at incredible speeds besides releasing thick, black and toxic fumes.
Sprays and
aerosols of such liquids can also result in hazards if there are sources of
high temperature in close vicinity. Any spill of such liquids also poses a
potential fire hazard as it flows easily and can spread across work benches and
laboratory floors. Such spills need to be cleaned up on priority to prevent
fire hazards.
Insidechem/lab-training
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