Technical information

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• Always store flammable liquids away from oxidizers.
• Be aware that liquids with flash points at and above 100oF may also present a significant fire
hazard in case of ignition.
Procedures for Reactive Chemicals
Reactive chemicals are substances which may enter into violent reactions with the spontaneous liberation
of heat and/or gases too rapidly to be safely dissipated. This may result in the rupture of the container, an
explosion, fire or the release of toxic gases/vapors.
Laboratory users should handle reactive chemicals with all proper safety precautions, including segregation
in storage. For example, nitric acid (a good oxidizer) should not be stored with flammables. Water reactives
should not be stored in a location where the item could get wet. Users should not mix for the first time even
small quantities of such reactive chemicals with other chemicals without prior approval of the Laboratory
Supervisor.
For hot perchloric acid digestions, use only a perchloric acid hood, or use special scrubbers approved by the
MIT Environmental Medical Service. This is necessary because the condensation of hot perchloric acid
vapors inside the hood can result in the formation of explosive compounds that are shock sensitive.
Picric acid is useful for revealing grain boundaries and carbides in steels; however, it becomes highly
explosive when it crystallizes out of solution during long-term storage (picric acid anhydride is an
explosive). Therefore, the solution should be discarded within one week of preparation. If picric acid
crystals must be used, procedures should be established to keep the crystals moist with water. Dry picric
acid crystals are a shock sensitive explosive.
Some chemicals on aging form reactive compounds. For example diethyl ether forms peroxides that may be
violently explosive. Thus, ether has an expiration date. Limit quantities of such materials and have a
notification system so that outdated quantities of ether are collected by the MIT Safety Office.
Procedures for Corrosive Chemicals and Contact-Hazard Chemicals
Corrosive chemicals are those substances that, by direct chemical action, are injurious to body tissues or
corrosive to metals. Users of corrosive liquids should take special precautions so that direct contact does
not occur.
Hydrofluoric acid (HF) is an important example of this class of chemicals. HF is worth particular attention
because it is being used in several departmental laboratories, including a teaching laboratory, and because it
has some unusually dangerous features. It is both corrosive and a toxic chemical that is absorbed quickly
through the skin. Serious injury or death may follow exposure even in cases where the victim is not aware
of a chemical burn.
Local first aid in the laboratory in the case of almost all chemical exposures is confined to washing, eye
washing, and safety showers. The exposed person must then go immediately to the Medical department.
Hydrofluoric acid is the exception. After the initial washing, HF Antidote Gel (Calcium Gluconate) must be
applied immediately and massaged into the affected area. Then go to the Medical Department. HF Antidote
Gel is available from the Environmental Medical Service (3-5360). This gel must be available within easy
reach of the user, and the instructions must be read before this acid is used.
The clean up procedure requires that slaked lime be used for neutralization. This forms calcium fluoride,
which is not soluble in water. The neutralized slurry should then be collected with an absorbent spill pad,
and placed in a container for disposal by the MIT Safety Office.
Ventilation
Work with significant quantities of toxic chemicals that have low air concentration limits (Threshold Limit
Value less than 50 ppm), or that have high vapor pressures, should always be done in a hood. At nights and
weekends laboratory general ventilation is reduced and users should place special emphasis on performing
in chemical hoods all operations that might release significant amounts of chemicals and/or contact
Physical Plant (phone FIXIT) so that their general ventilation needs can be met.
Chemical hoods should provide a minimum face velocity of 90 feet per minute (average) at any working
height that will be used unless a different face velocity is approved by the MIT Environmental Medical
Service.
Laboratory employees should understand and comply with the following principles: