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

The probable cause of the explosion at the Pacific Ocean Science and Technology building on March 16 was a detonation of compressed gases within a portable metal cylinder, ignited by a spark within a digital pressure gauge.

The department classified the blast as accidental.

“The gauge was not meant to be … where it was,” said HFD Battalion Chief Terry Seelig at a news conference at UH.

According to a report released Monday, “The accidental cause of this explosion was caused by the detonation of compressed gases 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. When the off button was pressed, an electrical arc/spark created within the gauge detonated the flammable gas within the tank causing the explosion.”

Visiting researcher Thea Ekins-Coward of the Hawaii Natural Energy Institute was alone in the basement laboratory when the explosion occurred. She lost her right arm from just above the elbow.

Ekins-Coward, 29, a postdoctoral fellow, was working on a renewable-energy experiment with a mixture of gases contained in the cylinder.

Two security guards and a graduate student kicked open the lab door and saw Ekins-Coward sitting on the floor, the report said. They quickly applied a tourniquet before paramedics arrived. Ekins-Coward told investigators she did not hear any sounds indicating leaking gases from any of the fittings or the pressure relief valve.

She was hired in October to conduct research in bioplastics and biofuels. The tank, gauge, pressure relief valve and fittings were purchased between November and January. After the tank was assembled, a pressure test detected leaks, and the tank assembly was taken to one of the university’s maintenance shops, which stopped the leaks.

Ekins-Coward told investigators that earlier in the week she had conducted another experiment using an air tank assembly nearly identical to the one that exploded. Both tanks used a similar mixture of gases and pressure gauge.

When she pressed the off button, a small internal explosion occurred, the report said.

She informed a researcher who hired her about the explosion and was told not to worry about it, according to the report. The lab where the explosion took place is operated by HNEI researcher Jian Yu.

At the news conference, UH spokesman Dan Meisenzahl said the small explosion went unreported to officials beyond the laboratory. “It should have been reported.”

Ekins-Coward told investigators it was “the first time the use of premixed gas in a portable tank to conduct experiments was being done,” adding, “In the past, each individual gas would have a separate hose line and be premixed at the reactor, eliminating the use of a portable tank.”

An independent investigation into the blast is being conducted by the University of California Center for Laboratory Safety. It is expected to complete the investigation by the end of the month.

“We’ll have a more comprehensive understanding of what exactly happened when this investigation is complete,” Meisenzahl said. “This was a wake-up call not just for UH, but labs across the country.” UH is establishing a new chemical and physical safety committee to help identify and implement protocols to further strengthen safety at laboratories on campus.

The lab underwent its annual inspection in January. Meisenzahl said the tank that exploded was set up in February.

The Fire Department report indicated investigators noticed in a follow-up investigation that the Ashcroft 300 digital gauge was missing, as was the gauge cover. UH had hired a cleanup company to decontaminate the lab.

Meisenzahl said only the gauge cover is missing and that the rest of the gauge components are accounted for. “It’s not a question of whether this particular gauge was faulty. It’s a question of whether this gauge is appropriate for this use.”

The Fire Department based its findings on the make and model of the gauge, not the specific gauge in the explosion, he added.