One of the potential hazards we may face at Fermilab is an oxygen deficiency hazard (ODH), in which another gas displaces the oxygen in the air we need to breathe. This can occur when, during a leak in a cryogenic system, a volume of liquid helium, nitrogen or argon or other substance turns to gas, expands in volume, and displaces breathable oxygen in the space.
Fermilab engineers analyze spaces at Fermilab to assess the ODH risk of the area and assign a risk classification system. ODH Class 0 is the lowest risk, while ODH Class 1 and ODH Class 2 are progressively higher risks. Fermilab requires workers entering ODH 1 and ODH 2 areas to take additional safety measures, including specialized ODH training and carrying a personal oxygen monitor to warn them of low oxygen content.
Some areas have been designed to achieve a lowest-risk oxygen deficiency hazard classification of ODH Class 0 even though oxygen-displacing fluids may be present. This is accomplished by addressing risks with active, engineered control measures. These areas use fixed oxygen monitors to continuously monitor oxygen content. Should low oxygen be detected, audible whooping alarm and flashing lights will alarm, and the system will take appropriate action to minimize the hazard, such as automatically starting ventilation fans to bring in fresh air. The whooping alarm means all personnel must leave the area.
No specialized ODH training is required to enter an engineered ODH Class 0 area, but one must be aware of the appropriate response to an activated ODH alarm. Fermilab is now posting caution signs for areas that rely on engineered controls to prevent oxygen deficiency hazards. These signs alert personnel of the potential hazard and inform them of the required evacuation response in the event of an alarm.
For those entering an area where an oxygen deficiency risk is present, one will see caution signs at entrances. Be aware of the differences in the ODH hazard classes. ODH 1 and 2 areas require special training, personnel protective equipment and medical qualification. ODH 0 areas do not require special training, just an understanding of the potential for the hazard, and to evacuate if the whooping alarm is sounded.
Always be aware of caution signs and what they say.
Bill Soyars is the chairperson of the Fermilab Cryogenic Safety Subcommittee.