More details on Argenta Hall explosions and recommendations

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RENO, NV (KOLO)-- The July 5 explosion that damaged Argenta and Nye halls was triggered by a smaller explosion in a boiler that destroyed a 3-inch gas line to the boiler, causing Argenta Hall to fill with gas and set the stage for the larger explosion.

A front view of Boiler #1 at Argenta Hall showing damage from internal explosion of the furnace assembly. the Nevada Division of Industrial Relations photo.

That’s the conclusion in the report on the explosion issued Tuesday by Brennan Paterson, chief administrative officer for the mechanical compliance section for the Nevada Division of Industrial Relations. It is one of the reports that will be filed in the investigation into the explosion.

The 13-page report summarizes what inspectors found at Argenta Hall and makes conclusions based on that evidence. It includes pictures of the damaged boiler and facilities.

A boiler mechanic attempted several times to restart the boiler after replacing a servo-controlled gas metering valve on Boiler #1, the report said. It appears a purge fan meant to remove fuel was not on, the report said. The explosion damaged the fan, so it could not be inspected.

“During the course of restarting the boiler, the furnace and exhaust assemblies of the boiler exploded in a fashion consistent with those assemblies having been charged with an unburned fuel and air mixture,” the report said.

The report also said: "Evidence is inconclusive as to the actual cause of ignition, though ignition may have been caused by the boiler igniter being actuated or by residual heat in the boiler as a result of previous attempts to start combustion."

The first explosion sheered a 3-inch gas supply line to boiler and there’s evidence that the line started burning like a torch, the report said.

About ninety seconds after the initial explosion, the sprinklers activated and it appears the water extinguished the fire, the report said. Gas continued to flow out of this line until the line was shut off at the street level about 10 minutes later, the report said.

The boiler room and adjacent elevator hoistway filled with gas, the report said. It’s not clear what ignited the larger explosion.

As a conclusion, the report said it is standard to have 3-inch gas lines close to boilers but if the line was placed away from the boiler it might have survived without being damaged.

“Additionally, the installation of an electrically controlled shutoff valve upstream of the boiler fuel train and away from the boilers, actuated by the existing emergency shut-off switch at the entrance to the boiler room, would have stopped the flow of gas into Argenta Hall upon actuation,” the report said.

The report said it will recommend Nevada Administrative Code be amended in the future to include these changes.

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Argenta Hall elevator hoistway, as seen from the roof of Nye Hall. Damage is consistent with a significant blast pressure wave caused by a gas explosion. Nevada Division of Industrial Relations photo.