COLUMBIA — Researchers in the MU lab where an anaerobic chamber exploded June 28 weren't following the chamber manufacturer's instructions and mixed hydrogen and nitrogen gas themselves instead of using premixed gas.
Four people were injured, one requiring brief hospitalization.
Friday afternoon, the Columbia Fire Department and MU released the findings of their investigations into the explosion in MU biochemistry professor Judy Wall's Schweitzer Hall lab on June 28.
Both investigations found that the accidental explosion started after hydrogen gas was introduced into an anaerobic chamber and an ignition source inside the chamber ignited it.
But the real culprit was researchers' practice of mixing their own gases to save money instead of using premixed gases — a practice that will now cease, according to Wall and the university.
Researchers were washing the interior of the chamber with what they thought was pure nitrogen gas. But it was actually a mixture of hydrogen and nitrogen because a tank containing hydrogen gas was connected to the nitrogen gas and left open, resulting in a potentially explosive level of hydrogen collecting in the chamber. The chamber contained several potential ignition sources including a heater, a fan and a catalyst material that produces heat. Fire investigators were not able to determine the exact cause of ignition, according to the fire department release.
According a press release from the MU News Bureau, the standard operating procedures for removing the oxygen from the chamber call for using nitrogen to fill the chamber. Then a small amount of hydrogen is added to create a reaction with any remaining oxygen, or oxygen that seeps into the chamber, to create water.
Brian Coy of Coy Laboratory Products, the company that manufactured the chamber, said that the company recommends using only premixed gases. And, he added: "We never recommend using pure hydrogen."
The chambers are labeled with warnings against using flammable gases like hydrogen on the front and back. The labels also recommend using only premixed gases.
Wall said she was aware of the manufacturer's guidelines.
"We did not deliver gas to the chambers in accordance with the manufacturer's instruction because we were mixing our own and had for 27 years," she said.
Wall said that premixed gases are more expensive and that using them might result in her lab doing less work, "but we'll be doing it with mixed gases."
The MU release said the hydrogen was introduced into the chamber because the valve for the hydrogen cylinder was left open after a check for leaks in the hydrogen gas lines. Also, the laboratory was using a T-connection that had a toggle switch in order to prevent nitrogen and hydrogen from entering the chamber at the same time. At the time of the explosion, a T-connection without a toggle switch was being used. That allowed both nitrogen and hydrogen to enter the chamber.
Wall said her lab aimed for less than 5 percent hydrogen when they mixed their gases. She also said that no warning systems were in use at the time of the explosion.
Several years ago, the lab purchased an oxygen and hydrogen monitor, but it was damaged by a corrosive substance produced by the microbes she studies. That resulted in incorrect readings.
Now, oxygen and hydrogen sensors will be used during the setup of the chamber, she said.
The university recommended the following actions to prevent future accidents:
- Replace the use of pure hydrogen with a 95:5 mixture of nitrogen and hydrogen.
- Following a check of gas lines for leaks, all gas cylinders should be closed and only reopened as needed.
- Use of T-connections between gases should be eliminated.
- Investigate the possibility of using hydrogen and/or oxygen sensors that could withstand a corrosive atmospheric environment.
- Give refresher training to all laboratory personnel. (Some training has already occurred.)
- Review current training, guidance materials and inspection procedures.
- Review MU's compressed gas cylinder storage area to ensure appropriate safety procedures are in place and look for improvements.
Wall said that she and her researchers have already completed a training session with Airgas, which is a specialty gas distributor. She also said that she and the lab staff are generating internal protocols to prevent future incidents.
Wall and her team were studying anaerobic bacteria that cannot live in the presence of oxygen. The bacteria converts toxic metals, such as uranium, to less toxic forms. Wall said that the bacteria are found in the soil that people walk across every day and did not pose an airborne danger after the explosion.
The MU News Bureau release said that the bacteria could be used by agencies that clean sites contaminated with radioactive materials or other toxic metals. Wall has already resumed her research, which is funded through a grant from the U.S. Department of Energy.