Defrosting a Laboratory Freezer

Preparing for the Defrost

• Notify your DSC and EHS representatives ahead of time about when you will be starting the defrost so they can be ready for unexpected situations to arise and so they'll know what to expect in the area.

• Ask everyone in the lab go through the entire unit and remove all unwanted samples and containers. If it is a combination refrigerator/freezer, the refrigerator portion also needs to be emptied.

• Designate an alternate freezer (and fridge if necessary) for temporary storage have everyone move all the stuff they want to keep to the alternate location.

• Be firm and set a deadline. Let people know that any remaining personal samples will be thrown out!

• Be sure to keep track of where everything is! Use stickers/post-its on the outside of the temporary storage indicating what's inside and where.

• Let everyone know where the temporary storage is with a sign near the unit to be defrosted.

• Check carefully for any damaged, leaking, or broken containers when emptying the unit.

  • If there's reason to believe that there is chemical contamination in the fridge, work with the waste management group to determine if you need to dispose of the melt water as hazardous waste.

  • If there is reason to believe there is biological contamination, contact the lab's biosafety group for guidance as well.

  • If the unit was used for radiological material storage at any point, work with the lab's radiation protection group from the start to plan, monitor, and execute the work and prevent any potential spread of radiological contamination.

Before Unplugging the Unit

• Remove any shelving or plastic storage areas (assuming they're not trapped in the ice).

• If you still have the manual for the unit, look for information about how the unit drains when defrosting. There may be a drain pipe built in to direct the water to a specific location, or the manual may tell you what to expect.

• If there is a dedicated defrost drain, be sure to get a large container under it.

• Place shallow pans, absorbent papers, and/or towels under and around the freezer to catch water. You can purchase special floor mats that absorb water.

  • The blue variety of absorbent mats with plastic on the underside are not the best choice, even though they’re the ones you see most commonly in front of fridges and freezers. You can purchase thicker mats that have no plastic and thus can absorb larger amounts of fluids. These are a better option than towels when it’s a lab fridge because they’re disposable.

  • BEWARE! Different freezers melt in different ways. Usually, the ice thaws and comes out the front as a puddle but some freezers thaw and melt out the back! If you’re not sure, check your manual or prepare for both possibilities. It may be necessary to pull the unit away from the wall.

Unplugging and Defrosting

• Schedule the work so that it starts as early as possible in the day, and be sure to check back frequently to empty trays, change absorbent pads, and rescue samples or containers that may have been completely enclosed in the ice.

  • If shift work is possible, try to have someone scheduled who can stay later into the evening so that you can be certain there's nothing left in the unit and it won't cause a flood before anyone leaves it alone.

• Check the area around the unit for any equipment that might be damaged by pools of water, especially electrical equipment, which may short and cause a fire. As much as possible, move everything near the unit up off of the floor where it won't get wet or damaged.

• After unplugging the unit, tape the cord off the floor so it doesn’t get wet, stepped on, or tripped over.

• Leave the door(s) open (unless the manual directs otherwise) for as long as it takes for all the ice to thaw. Use a bin/prop to hold doors open if necessary.

  • For doors that are higher up, you can use a folded wad of paper towels (or cardboard) jammed between the two-door hinges to force the doors to stay open. The towels can be reused later when you’re mopping up the inside of the freezer or cleaning the fridge.

• Check on the freezer regularly to empty pans, change out absorbent pads, and mop up any puddles that may cause damage or cause someone to slip. Put up an obvious sign if possible, to warn others that the floor may be wet.

• If you have some time and the freezer needs to be back in order quickly you can speed up the process with a hairdryer, a fan, or a heated spatula pressed to the ice.

  • Beware of electrical equipment around water! If you decide to use a hairdryer or a fan, keep the hairdryer/fan and its cord and plug away from ice and water. Ensure that you are standing on dry floor while operating the hairdryer or fan.

  • Do not chisel at the ice with anything sharp, as it may damage the freezer.

• For refrigerators in laboratory areas, if the ice is particularly thick, you may find surprises buried in the ice, such as small chemical containers or old samples. This is another reason not to try chiseling at the ice.

• It is recommended to wear gloves when replacing or removing the absorbent pads in case there is any contamination.

• If at any point during the thaw you see something unexpected, such as a broken container that was completely enclosed in the ice, contact your Division Safety Coordinator and EHS representatives for help.

After the Defrost

• Once the ice has melted, wipe the insides of the unit down to ensure they’re completely dry. If you leave them wet, the ice will come straight back.

• Clean the unit if it is dirty. Baking soda and hot water work, or for a more intense clean, use 10% bleach solution.

• When moving things back into the unit, take the opportunity to do a quick chemical inventory and reorganize things with clear labels.