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Environmental Health and Safety

Laboratory Refrigerators and Freezers

Refrigerator and Freezer Hazards

The potential hazards posed by laboratory refrigerators and freezers involve vapors from the contents, the possible presence of incompatible chemicals, and spillage. Loss of electrical power can produce extremely hazardous situations. Flammable or toxic vapors may be released from refrigerators and freezers as chemicals warm up and/or certain reactive materials may decompose energetically upon warming.

Refrigerator/Freezer Labeling

Refrigerators and freezers should be labeled clearly for their intended purpose (e.g., “No Food or Drink to be Stored in this Refrigerator”, “Refrigerator For Food Only”, "NO FOOD - CHEMICAL STORAGE ONLY", "Not For Flammable Storage", etc.).

Flammable Liquid Storage

Standard "domestic" refrigerators have thermostats inside that control electrical fans and motors.  These are potential ignition sources for flammable vapors. Therefore, flammable chemicals or chemical mixtures that must be kept below room temperature must be stored in refrigerators or freezers specifically designed by the manufacturer to be explosion proof. Flammable liquid-approved refrigerators are designed with spark-producing parts on the outside to avoid accidental ignition. If refrigeration is needed inside a flammable-storage room, you should use an explosion-proof refrigerator.

All other refrigerators or freezers not specifically designed to be explosion proof should be labeled with a prominent warning sign indicating that they are unsuitable for the storage of flammable substances. Electric heaters used to defrost the freezing coils can also spark. To ensure its effective functioning, a freezer should be defrosted manually when ice builds up. Frost-free refrigerators should also be avoided since many of them have a drain tube or hole that carries water, and possibly any spilled materials, to an area near the compressor, which may present a spark hazard.

Explosion-Proof Units

Here is the difference between the two types:

  • Flammable storage refrigerators and freezers have no exposed ignition sources inside the cabinet, such as lights or switches, that could ignite vapors.  (like an auto defrost device)
  • Explosion-proof or spark-proof units have no interior or exterior ignition sources. An explosion-proof refrigerator or freezer may be required in rare circumstances in hazardous locations.

You do not need an “explosion-proof” fridge unless you are in a lab with the potential for reaching lower explosive limits for vapors concentrations.  This might the case with a large spill – especially in poorly ventilated areas.   You a flammable storage unit for lab chemical storage.  We like to see non-residential units used in chemical labs (wet labs) because it avoids mis-use and confusion.  It allows flexibility in future uses. 

However, if you do not store flammable chemicals and you label the unit no food or beverage and also “no flammable chemical storage”, you can keep regular units for bio samples.

Another consideration is older units with defrost cycles (or when you manually defrost) can leak water into the unit.

Refrigeration/Freezer Contents

All materials in refrigerators or freezers should be labeled with the contents, owner, date of acquisition or preparation, and nature of any potential hazard. All containers should be sealed, preferably with a cap, and placed in secondary containers or catch pans. Since refrigerators are often used for storage of large quantities of small vials and test tubes, a reference to a list outside of the refrigerator could be used. Labels and ink used to identify materials in the refrigerators should be water-resistant.

Preventing Refrigerator/Freezer Explosions

Flammable liquids must only be stored in refrigerators which have no internal ignition sources. To prevent refrigerator and freezer explosions, lab supervisors must vigorously enforce the following:

  • All materials with a flashpoint below 100° F may only be stored in a UL approved flammable materials storage refrigerator or freezer. These units do not have any internal ignition sources.
  • All ordinary domestic refrigerators and freezers should be labeled with the phrase “No materials with a flashpoint below 100° F may be stored in this refrigerator/freezer” or “Not for flammable storage.”

To see an example of the extensive damage a refrigerator explosion can cause, click here.

Below is an example of signage of proper refrigeration in the laboratory and an example of a fridge with exterior spark producing parts to prevent explosion.

friddge4  thermostat


For additional information about selecting appropriate refrigerators and freezers, storing flammable chemicals and chemical compounds with low flash points, or proper labeling for laboratory refrigerators and freezers, contact EH&S.