Solvent Refrigerators and Freezers

Freezers and Refrigerator use in Laboratories

Use of domestic refrigerators and freezers in laboratories is potentially dangerous. Appropriate selection of refrigeration units is critical to prevent fire, or explosion.  This equipment guide describes types of refrigeration units and appropriate use of each device with respect to chemical, biological, and radiological materials.  Human Food should never be stored or used in a laboratory.

 

Background:

The possibility of igniting vapors from flammable liquids is the primary concern driving the use of special equipment.  The National Fire Protection Agency issues regulations pertaining to flammable liquids and their use.  NFPA 45 covers fire safety in laboratories while NFPA 30 covers the use of flammable materials in general.  NFPA defines a flammable liquid as having a flash point of less than 100°F (38ºC). Materials meeting this definition are likely to form ignitable vapors and hence require special equipment.

Below is a small list of some common laboratory solvents and their flash points. A more complete list of flammable chemical can be found at ACS, Division of Organic Chemicals6. You should always consult the SDS sheet before placing flammable liquids in refrigeration devices to assure you have the right type of device.

Table 1. Chemicals to Never Store in a Domestic Refrigerator

 

Chemical

Flash point (°F)

Chemical

Flash point (°F)

Acetone

4

Methanol

54

Acetonitrile

42

Petroleum Ether

20

Benzene

12.2

n-Pentane

−49

Butanol

84

Propyl Alcohol

74

Cyclohexane

−4

Pyridine

68

Cyclohexene

10

Sigmacote

25

Dioxane

54

TEMED                                       

50

Ethyl Acetate

24

Tetrahydrofuran

6

Ethyl Alcohol

55

Toluene

40

Ethyl Ether

−49

Triethylamine

20

Hexane

−7

Trimethylpentane

19

Isopropanol

53

Xylene

84

       

These common solvents have flash points close to or below the temperature at which most refrigerators operate (around 39°F or 4°C). The items in the door of your refrigerator can easily get as high as 59°F or 15°C.  Flammable solvents evaporate rapidly, even at lowered temperatures, so they can quickly reach equilibrium inside the small, well-sealed space of a refrigerator. When this “off-gassing” reaches the lower explosive limit (LEL), sources of ignition inside a conventional refrigerator such as the thermostat, interior light, defroster, compressor, or fan can set off an explosion. Even closed containers can create enough vapors to cause an explosion. Flammable liquids that must be stored at reduced temperature require a specially designed refrigerator, termed a “flammable material storage refrigerator,” where ignition sources are isolated from the inside space. See the following paragraphs for an explanation of the different types of units available.

 

Three Types of Refrigerators/Freezers

Three basic types of refrigerators/freezers exist.  Usage depends on the level of hazard and materials in use.

 

  1. Household (Domestic): Refrigerators and freezers that can be used in laboratories for storage of aqueous solutions and nonflammable/non-explosive materials.  A hazard analysis of the work in a laboratory is also required to make sure that there are no flammable vapors in the laboratory itself that could ignite.  An example of this might a biology lab storing samples of tissue in a non-flammable liquid were no other hazards are present in the laboratory space. A domestic refrigerator is appropriate in this instance. One last point with domestic refrigerators is that they tend require more maintenance.  Failure to clean the heat exchange coils regularly can result in failure and fire.  The seals also tend to fail quickly from exposure to chemicals.

 

  1. When the hazard is inside the refrigerator rather the laboratory itself, Lab-Safe (or Explosion-Safe or Flammable), devices that are considered “spark safe” are sufficient.  These devices are designed so that all sources of ignition such as lights or switches are removed from the interior of the refrigerator.  These devices cannot be used in a room where flammable materials are in use such that the risk for ignition is present.  Most laboratories will meet this level of protection and this is the most common level in use.  These devices must be manufacturer and UL approved for this use.  Simply unscrewing the light in a domestic refrigerator is insufficient.

 

  1. Explosion-Proof: Refrigerators are devices that have all sources of ignition sealed both inside and outside the device.  These type of devices are required in spaces where a large amount of work with flammable solvents or other materials exist that could be ignited. Explosion-proof refrigerators feature enclosed motors and are labeled with an FM®(Factory Mutual) or UL® (Underwriters Laboratory) explosion-proof label.  Such refrigerators must also meet the requirements for Class 1, Division 1 Electrical Safety Code (NFPA 45 and 70) and require direct wiring to the power source via a metal conduit.

 

All types of refrigerators/freezers should be frost-free to prevent water drainage or damage. The refrigerator/freezer must meet all applicable codes (i.e., National Electric Code- C11; NFPA 45, 56C, and70; and, OSHA 29 CFR 1910.30).

 

Results of improper storage of flammable liquids.

Fires and explosions have occurred when flammable vapors built up within a standard refrigerator, freezer or cold room. Vapors from materials inside the unit ignited by the unit’s unprotected mechanical or electric components caused explosion. Severe damage occurred that resulted in down time, injury, media attention, and regulatory investigation

 

Figure 1. Three incidents from the University of Vermont, University of Virginia and Michigan State University are shown below. The explosions were both due to storing flammables in conventional refrigerators.

Picture of Exploded Refrigerators

The following excerpts below demonstrate that It didn’t take a lot of vapors to ignite and create an explosion.

Michigan State University: https://ehs.msu.edu/news/2015-07-10-fridge-explosion.html

A container of flammable liquid stored in a household refrigerator found an ignition source inside of the unit. The refrigerator door was blown across the room, windows broken, and the contents of the fridge scattered  

 University of Vermont: http://www.uvm.edu/safety/lab/refrigerator-explosion

Isopentane (2-methylbutane), 100 mL, was placed in an unsealed container in a typical household refrigerator. A spark caused an explosion of the flammable vapor. The force was large enough to blow off the door to the refrigerator and break the windows more than 20 feet away.

University of Virginia: http://www.sciencemag.org/careers/2006/08/lab-safety-requires-training-and-commitment

At the University of Virginia, organic chemistry students were storing samples they prepared in an unlabeled refrigerator that was not explosion proof. When the refrigerator exploded, the doors to the main lab were blown to the other side of the room where they hit an apparatus used to purify solvents.

 

Proper Signage of Refrigerators/Freezers

Prudent Practices for Research Laboratories, the National Academy of Sciences, and OSHA state that the storage of food and beverages in refrigerators containing chemicals is unlawful.  The potential for contamination of food and subsequent ingestion is unacceptable.  Refrigerator/freezers must have appropriate signage. Examples of such signage include:

 

  1. Domestic Refrigerator/Freezer Signage used in the laboratory:

          "No Food and Drink" / "Flammable Materials Prohibited”

  1. Spark Free Refrigerator/Freezer Signage:

          "Flammable Materials Permitted" / "No Food or Drink"

  1.  Explosion-Proof Refrigerator/Freezer Signage:
    "No food or Drink" / "Approved for Use in Hazardous Locations" / "Flammable materials Permitted"
     
  2. Examples of manufactures labels for conventional, flammable storage and explosion proof refrigerators:
    Types of Refrigerators
  3. American Chemical Society, Division of Organic Chemistry:

    Common Organic Solvents:

                           https://www.organicdivision.org/wp-content/uploads/2016/12/organic_solvents.pdf

 

 

Questions

If there are any laboratory refrigerator health and safety concerns or questions, please contact EHS at 368-2907.