Health and Safety,Regulations

Cryogenic materials of one sort or another are used in many labs in support of animal areas across the country, and also out in the field, freeze marking or freeze branding animals. We may receive shipments packed with dry ice, preserve samples with liquid nitrogen, keep our equipment cooled, and in some cases, use techniques that employ cryogenic liquids, such as marking animals in zoological, husbandry, or natural settings.

As with most things we discuss, all of these can be done safely if we recognize the hazards and work diligently to control them. As we scan the literature, there are differing opinions on when a substance becomes a cryogenic material. We will consider materials with boiling points below 75°C (so as to include dry ice) as cryogenic for our discussion. ¹

Cryogens are similar to other broad classes of chemicals in that we can divide the concerns into physiological hazards and physical hazards. As with other chemicals in the lab, it should go without saying that the MSDS should be reviewed and SOPs developed for inclusion in your chemical hygiene plan.

Physiological Hazards
Physiological hazards can be grouped into two main divisions: those that damage tissue from direct contact, and those that can cause asphyxiation.

Direct Contact
Rule number 1—Protect your skin and eyes. Those of us who are old enough and have spent a lot of time in the sun in our youth are all too familiar with the effects of liquid nitrogen from our visits to the dermatologist. The quick, controlled spray of liquid nitrogen freezes and kills tissue in pretty short order. The same effect is true from accidental splashes or contact with these very cold materials. Always wear eye protection whenever you are near a cryogenic liquid or working with samples recently removed from cryogenic temperatures. In addition, also wear a full-face shield if a cryogenic liquid is poured, or if an open container of the cryogen may boil and splatter. To reduce the amount of splatter when transferring cryogenic liquids from one container to another, always start slowly to allow the vaporization to chill the receiving container as you are filling it. After the vaporization and liquid boiling has decreased, fill the container at the normal rate.²

Cryogenic materials flow freely as do other liquids and, as a result, can splash and spill. It is important to wear liquid-resistant gloves to prevent splashed liquid from being absorbed and freezing the skin.