July 11 (UPI) — One man is dead after fire inside a hyperbaric chamber in Lake Havasu City, Ariz.

It’s the second such fatality in the United States this year.

The 43-year-old died after the “flash fire” earlier this week, officials confirmed in a statement on the city’s website.

The man was later identified as Walter Foxcroft, a physical therapist and founder of Havasu Health and Hyperbarics.

The cause of the fire remains under investigation.

Officials said it wasn’t immediately clear why Foxcroft was in the chamber, which can be used to treat a variety of conditions.

Fire crews initially responded to a 911 call of a fire at the facility.

Eventually, five engines from the Lake Havasu Fire Department responded.

“The first arriving crews identified smoke throughout the building and an intact hyperbaric chamber that appeared to have had a flash fire in the chamber with one patient inside. The patient was pronounced deceased upon arrival of emergency crews,” the city said in the statement.

In late January, a 5-year-old boy died following an explosion in a hyperbaric chamber at a medical facility in Detroit. The child was being treated in the chamber at the time of the explosion at the Oxford Recovery Center in Troy, Mich.

Hyperbaric chambers contain 100% oxygen, which is up to three times the amount in a normal room, making them susceptible to fires.