At an oxygen concentration of 19 percent some physiological effects will start to occur; however, these won't always be noticeable. Between 15 and 19 percent thinking will become impaired, along with coordination. A reduction in intellectual performance ensues typically without awareness, just when you potentially need to make life saving decisions. At 12-15 percent you will experience poor judgement and abnormal fatigue; this will increase as the levels drop to 10-12 percent, and there is a distinct possibility of fainting within just a few minutes. If levels drop below 10 percent a typical person will experience an inability to move, loss of consciousness and convulsions followed by death in as little as nine minutes.
So, what situations can cause an oxygen depleted atmosphere? Oxygen deficiency normally occurs in an enclosed space and can be caused for a variety of reasons. Where there is a volume of gas, be that in a tank or pipeline, leaks can quickly fill an enclosed space displacing the oxygen. Another cause is decomposition of organic matter, plant or waste material for instance emit carbon monoxide, carbon dioxide and potentially hydrogen sulphide, these displace the oxygen and, in some cases, react with the oxygen resulting in an oxygen deficient environment.
According to the Health and Safety Executive (HSE) a confined space is defined as: A place which is substantially enclosed (though not always entirely) and where serious injury can occur from hazardous substances or conditions within the space or nearby (e.g. lack of oxygen).
As such, you would be excused for thinking that a laboratory or room wouldn't require an oxygen monitor. However, there are scenarios where a room oxygen monitor would be required - if you consider a cryogenic lab for instance, many litres of liquid nitrogen are stored within the freezers. Given that liquid nitrogen expands by 694 times upon evaporation, it's easy to see how a leak could quickly displace the oxygen within a room rendering it deadly. In fact, the Occupational Health and Safety Administration (OSHA) regulations require that any room where compressed gases are used or stored are fitted with oxygen deficiency monitors.
Monitors, when properly functioning, should measure the oxygen concentration within the room and alarm if it should dip below 19.5 percent. Therefore, remembering that every gas detector is only as good as its last calibration, it is important to regularly function test and calibrate at the prescribed interval period. A quality calibration gas is never far away, Air Products offers lightweight canisters of all common calibration gases on their online store ready for immediate despatch: airproducts.expert/uk/oneuse