The Occupational Safety and Health Administration is now looking into an explosion that rocked Erie Middle School and the surrounding neighborhood Wednesday.Fire investigators said three people suffered burn and fall injuries when a plumbing company employee tried to re-light a hot water heater and a buildup of gas ignited.Fire officials told 7NEWS that that was the first time the gas line had been turned back on since the school expansion project began.When asked if Xcel Energy should have been called before the water heater was re-lit, Laura McConnell of Mountain View Fire Rescue said, Thats a good question. I know that our fire investigators are working on that as well.McConnell said that plumbers are generally qualified to work with hot water heaters, but added that even experts sometimes run into situations that they dont anticipate.The explosion knocked out walls and ruptured the ceiling of the gymnasium.We heard this giant explosion, said neighbor Philippe Bryant. We were driving around the corner and saw all this paper flying out the door.Bryant said he was working on Wall Street during 9/11 and that all the paper fluttering from the school reminded him of the World Trade Center.It was not a good reminder, he said.Bryant told 7NEWS that an employee in the school said there is a lot of pressure to get the construction work done before school starts.School starts Aug. 16.Bryant said, Ive heard there have been screaming matches and that workers have been told, Hurry it up, get it done.St. Vrain Valley School District spokesman John Poynton told 7NEWS that he cant comment at all about the investigation, but said the gymnasium will remain off limits until the conclusion of the investigation.He said even district officials cant get in to assess the damage.Until we can get in there, we wont know how long it will take to repair, how much it will cost or whether it will be done before school starts in two weeks, Poynton said.McConnell said fire investigators dont want anyone in the gym until they have a chance to talk to the injured workers.We want to find out where they were in the gym, McConnell said. We dont want anything disturbed at the scene until then.McConnell said they hope to talk to the victims over the next two or three days.She said one of the injured workers was treated and released Wednesday, a second victim has been upgraded to serious condition and a third victim remains in critical condition.