Hydrogen Safety
 The photograph on the left was taken inside of a university laboratory in Missouri after a mixture of hydrogen and nitrogen exploded inside of an incubator. Although the explosion occurred in 2010 it still serves as a timeless reminder of the explosive potential that hydrogen possesses.
The Explosive Range is the range of a concentration of a gas or vapor that will explode if an ignition source is introduced.
Below the explosive range the mixture is too lean to explode and above the upper explosive or limit the mixture is too rich to explode. The limits are commonly called the "Lower Explosive Limit" (LEL) and the "Upper Explosive Limit" (UEL).
Hydrogen is unique in that it has an extremely broad explosive range. Gasoline, for example, has an explosive range of 1.4%-7.6%. This means gasoline will not explode if the concentration is too lean to explode if the concentration is less than 1.4%
and too rich to explode if the concentration is greater than 7.6%. Hydrogen has an explosive range of 4%-75%. This means that concentrations of hydrogen as high as 75% will still explode.
 This explosion occurred in an anaerobic incubator.
The laboratory was studying a bacteria that is intolerant to oxygen so the incubator is first purged with nitrogen after which a small amount of hydrogen is introduced which acts as a desiccating agent by binding with the oxygen and is removed from the atmosphere in the form of water.
The hydrogen and nitrogen cylinders were connected to the incubator with a "T-connection" with a toggle switch which prevents nitrogen and hydrogen from entering the incubator simultaneously. At the time of the explosion, it was discovered that the toggle switch had been removed and a simple T-fitting had been used as a temporary replacement.
The hydrogen gas was opened for a leak check and was inadvertently left open. Without a toggle switch in place, the hydrogen gas freely flowed into the incubator and an unknown ignition source detonated the mixture.
The photograph below is of the exterior of the science building. As you can see the force of the explosion was so great that it not only destroyed the laboratory but also blew all the windows out of the laboratory. The explosion injured 4 people who were in the lab at the time of the incident. All have recovered without permanent damage.
Accident investigators recommended the following actions to prevent a repeat of a similar accident in the future:
- Replace the use of pure hydrogen with a 95:5 mixture of nitrogen and hydrogen.
- Ensure all cylinders are closed immediately following a leak check.
- Eliminate T-connections between gases.
- Investigate the feasibility of placing hydrogen sensors inside of the incubator.
- Provide laboratory safety refresher training to all laboratory personnel.
- Review training, guidance materials and the laboratory inspection process.
- Review the compressed gas cylinder storage area to ensure appropriate safety procedures are in place as well as look for improvements.
We offer hydrogen safety training in an online format on E Train so please use this accident as a learning tool, take our online hydrogen safety training and put into practice what you have learned.
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