Oxygen-deficiency hazards

This sign marks areas at Fermilab with higher-than-normal ODH risk. Entering such areas requires training and adherence to special procedures.

What does ODH stand for?

A. Ohio Department of Health
B. Order of the Dark Hand
C. Old Dominion Hounds
D. Oxygen Deficiency Hazard
E. All of the above

The correct answer is E, but at Fermilab the answer that matters is D. Most of us are aware of the low-oxygen hazards at high elevations, either in the mountains or during airline travel. Oxygen displacing gases can have the same effects as high altitude.

Oxygen deficiency can have serious consequences. At workplaces in the United States, the average annual fatality rate from oxygen-deficient atmospheres is 8.4 people. Fermilab, with its high awareness of the hazards of oxygen deficiency and its excellent safety assessment and training, has never suffered a serious oxygen deficiency injury.

In some areas of the laboratory, Fermilab uses large amounts of gases and cryogenic liquids that would displace oxygen if released into the air we breathe. When warranted, these areas are clearly posted with a sign such as that shown above.

Cryogenic liquids have the potential to fill large volumes with gas since they expand to 700 times their liquid volume upon release. To put this in perspective, a common 160-liter (about 42 gallons) nitrogen dewar could bring a 70-by-70-by-10-foot room below a safe level of 19.5 percent oxygen. Even large amounts of liquids and gases are safe, however, as long as they are contained and ventilation is provided. FESHM 5064 focuses on potential leaks into buildings and ventilation that could prevent the leaks from becoming dangerous. The risk of leaks, the ventilation system and the size of the room all factor into the ODH risk assessment.

Risk class 0 means the ODH risk is no greater than common workplace hazards.

Risk classes 1 and 2 are higher risks. Entering these areas requires training, oxygen monitors and adherence to other procedures to mitigate the hazard. These higher-risk areas are posted “Oxygen Deficiency Hazard” and are restricted to trained personnel.

For further information please see FESHM 5064 or contact us at rlschmitt@fnal.gov or sanders@fnal.gov.

Richard Schmitt and Bob Sanders, members of the Cryogenic Safety Subcommittee