In a preliminary estimate, there may have been some sort of problem with pressure in making a transfer. There have been lots of delays for investigators before they can get inside because there was a leaking methane cylinder, then it froze up when they were trying to drain it. Finally, it is now empty.
"For me it was a very loud explosion. That's what I heard and then there was a bit of commotion inside," said Bob Collier.
Collier works for a company with offices above the lab where the explosion happened.
"I felt it and felt the building shake. I heard an explosion," said Tim Hill.
Hill was in his office at Membrane Technology and Research when the explosion occurred in the lab down the hall.
"It was a big boom," said Hill.
He joined two dozen other employees in getting out of the building. A scientist had been mixing helium, methane and nitrogen into one cylinder when something went deadly wrong. And some of the people went to the aid of their fallen comrade.
"Five went into the laboratory, it was very risky to do that and it did have some positive effect because they did turn off other cylinders," said Menlo Park Fire Chief Harold Schapelhouman.
They pulled the man from the lab, he was still alive, but he died in front of the building. There was also a woman scientist in the lab who was blown out the door by the force of the blast.
"She was transported, as I understand it. Outside of the hearing and eardrum issues, more than likely from the over-pressure from the explosion in a confined area, she did have some medical issues, but according to her fellow co-workers at the time the complaint was minimal," said Schapelhouman.
The explosion has damaged the lab, including some water damage. Inspectors will have to determine if it is safe. The company does research on a filtration process for petrochemicals and natural gas, but the fire chief says there was never a hazard from the explosion.
"The nature of what they do here and the amount of product that they're able to use, there really isn't a risk to the local community or anyone outside the structure itself," said Schapelhouman.
Many are still wondering what could have caused this explosion and what role the leaking cylinder plays in the blast. That's what investigators will determine.
"I know the ins and outs and I can't think of what could have gone wrong at this point," said Hill.
Cal/OSHA is going to take the lead on this investigation. Because of the damage inside, investigators are red-tagging the building, which means nobody can get back inside until Monday at the earliest.