A powerful explosion at a University of Hawaii science lab was likely caused by a digital pressure gauge that shouldn’t have been used around flammable gases, the Honolulu Fire Department said today.

The probable cause of the explosion at the Pacific Ocean Science and Technology building on March 16 was a detonation of compressed gases sparked by a digital pressure gauge within a portable tank that was not designed for that use.

The fire department classified the blast as accidental.

Visiting researcher Thea Ekins-Coward, who was alone in the basement laboratory when the explosion occurred, lost an arm in the blast.

At approximately 5:51 p.m., Ekins-Coward, 29, a post-doctoral fellow, was working with a mixture of low-pressure hydrogen, carbon dioxide and oxygen when the portable metal cylinder the gases were contained in blew up. The lab is operated by the Hawaii Natural Energy Institute.

In the fire department’s report released today, investigators indicated a portable gas cylinder was the point of origin of the blast. An electrical arc/spark occurred from a digital pressure gauge.

“The accidental cause of this explosion was caused by the detonation of compressed gasses to include: hydrogen, carbon dioxide and oxygen within the air tank. A digital pressure gauge used to check the pressure within the tank was not rated or designed (not intrinsically safe) to be in a flammable gaseous atmosphere,” the report said. “When the OFF button was pressed, an electrical arc/spark created within the gauge detonated the flammable gas within the tank causing the explosion.”

The university has retained the University of California Center for Laboratory Safety to conduct an independent investigation into the blast. The three-member team is expected to complete their investigation by the end of April.