Working in Cold or Freezer Rooms

Working in Cold or Freezer Rooms

All workers in a cold room work area must read and signs and associated risk assessment before commencing work.

As cold room is essentially a big fridge, it is vital that the door is only kept open for short periods of time, therefore anyone wishing to carry out prolonged work must do so with the door closed. This, of course, leads to the necessity for strict safety precautions being taken when under taking work in the cold room.

  • No lone working – work inside the cold room must be carried out in pairs with a third person, who is aware of the work, outside of the cold room.
  • Timers/alarms – Two timers must be set when work commences, one to be kept inside the cold room and one to be kept by the third person. The timers will indicate the maximum time that the workers can stay in the room and when the alarm sounds the workers must take a minimum of 30 minutes break. The person outside of the cold room must ensure that the workers are out.


Cold Rooms in Labs

In the past, cold rooms for labs consisted of insulated boxes that did NOT have ventilation. Some of the newer cold rooms were provided with a small volume of fresh air to help ventilate the rooms. The supplied air was intended to prevent the buildup of carbon dioxide generated from personnel in the room as well as other contaminants that might be released in the room. Unfortunately, this small volume of supplied air created moisture problems contributing to mold growth, especially when trace contaminatns are present on surfaces. The result creates potential mold inhalation exposures for personnel.

Because cold rooms do not have ventilation systems, occupancy of cold rooms is limited to a total of two hours per 24 hour period (1 person for 2 hours, 2 people for 1 hour, etc.)


A number of health and safety problems can occur in cold rooms. These problems range from inhalation exposure of mold, unsafe use/storage of chemicals resulting in inhalation exposures, and storage of food and drinks in cold rooms resulting in potential ingestion exposures to molds. This document reflects good laboratory practices users of cold rooms are expected to follow.


The intention of cold rooms is to properly store certain agents and to conduct certain tests at a controlled temperature. Storing cellulose containing items can promote mold growth. Since biological and chemical agents are found in cold rooms, the potential for cross contamination of food and beverages can occur. To that extent, these guidelines are recommended to minimize mold growth, recommend correct chemical and biological use and storage, and list some activities that are prohibited.

Personnel can experience inhalation exposures to mold and a buildup of carbon dioxide when they are in cold rooms. Although the OSHA is for periods of 8-hours, its sometimes recommend personnel can occupy a cold room safely, based on the carbon dioxide level, for a period of 2 people-hours per day, to provide for variations in the size of the cold rooms.


Minimizing Potential Mold Growth

Mold has been found in many cold rooms. Every surface in a cold room can become contaminated with mold quickly should an improper work practice occur. The result is potential health problems from inhalation of the mold spores as well as contamination of research materials.

The storage of cellulose containing materials is a leading cause of mold growth. Mold growth can contribute to contamination of research materials. Preventing mold growth in cold rooms is achieved by controlling condensation/moisture and removing materials contributing to mold growth. The following actions need to be followed:

  • Promptly clean up spilled liquids (e.g., buffers, media). Mold can thrive on any organic medium.
  • Report water leaks.
  • Keep door firmly shut to prevent condensation. Doors left open can increase the relative humidity in the rooms and promote mold growth. Placing a relative humidity (RH) gauge in the cold room and maintaining the RH at less than 60% helps to discourage mold growth.
  • Damaged door gaskets can provide a cold surface resulting in condensation problems. Watch for condensation on other surfaces as well. Condensation may be an indication of a loss of containment.
  • Remove all wood. Wood shelves can absorb moisture and, because it is composed of cellulose, is a perfect breeding ground for mold. Wood shelves need to be replaced with open stainless steel shelves that permit air flow throughout the storage area.
  • Remove all cardboard and paper products. These surfaces act just like wood and promote mold growth. If some paper products are required, place them in a closed plastic container between uses. Should visible mold be found on a paper product, discard the item immediately.
  • Keep surfaces clean. Never use bleach on metal surfaces (bleach on metal surfaces can result in pitting). Wet cleanup activities are recommended (sweeping, dusting, or brushing will release mold into the air and can cause inhalation exposures and spread potential contamination).
    • If minor cleaning is needed, use a wet clean up method (e.g., dampen cloth with a non-ammoniated soap or detergent (do not mix ammonia and bleach; the fumes are toxic ). Dry surfaces after cleaning to ensure moisture has been removed.
    • If mold reappears soon after cleaning, use any hospital approved disinfectant, drying surfaces after cleaning to ensure moisture has been removed.
  • Place a label on the cold room door to remind users not to store paper/wood materials in the cold room as well as clean up small spills of materials soon after they happen.

Proper Chemical Use and Storage

Cold rooms are designed to recirculate the air contained within. Chemicals vaporizing into the air can accumulate and pose an inhalation exposure or an explosion hazard to personnel. Therefore:

  • Many flammable solvents can release sufficient vapors to form explosive atmospheres. These rooms have fans and electrical laboratory equipment that are potential ignition sources. Large quantities (>1 liter) of flammable solvents must NOT be stored in cold rooms. On a related issue, a standard refrigerator must never be used for the storage of flammable materials. Rather, flammable storage refrigerators need to be used.
  • Since cold rooms have a contained atmosphere, some hazardous chemicals that are not flammable may vaporize (e.g. chloroform, formaldehyde) causing exposures to personnel. The lab staff must consider this risk when evaluating the safety of their procedures and perform those procedures where vapors are released in a chemical fume hood. Quantities need to be limited to less than 250 ml (note: chemicals such as chloroform vaporize very quickly. Such chemicals should NOT be placed in squeeze dispenser bottles.
  • Spills of organic chemicals can occur in cold rooms. Prompt removal of the spilled materials is essential.

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