LYNN – Fires in flat-roofed buildings like the West Roxbury restaurant where two Boston firefighters died Wednesday prompted Revere’s chief to pull his crews from a burning auto body shop in July and a Lynn district chief to give a similar order in June.Lynn Fire Chief Edward Higgins said flat-roofed buildings, like the strip mall Chinese restaurant where the Boston firefighters were killed, are notorious for allowing fire to burn for a long time inside their lightweight construction. When firefighters enter the building to fight the fire, built up heat ignites fresh oxygen and triggers an explosion called a “flashover.””It builds up and everything ignites. We train and train and train, but a fire is a hostile environment,” Higgins said.Revere Chief Eugene Doherty said Boston firefighters may not have realized how long the fire was burning inside the restaurant’s ceiling. He ordered firefighters out of Modern Collision auto body on American Legion Highway out of fear the building’s ceiling would collapse on firefighters.Lynn District Chief William Curran ordered his men out of Raffi’s in June after assessing the fire burning in the bar’s ceiling.”He took the exact level of precaution,” Higgins said, adding, “In a strip mall type building, lightweight type truss construction is used. If one section fails, it all goes.”Even as they assessed the dangers fires like the Boston one pose, local chiefs ordered station flags lowered to half-staff and extended their sympathies to the fallen firefighters’ families.Swampscott Fire Department spokeswoman Jennifer Bleiker posted an expression of sympathy on the department Web site Thursday that read in part: “Our thoughts, prayers, and support go to our brother firefighters who gave their life for their mission.”In addition to the two firefighters who were killed, Boston Fire Department spokesman Scott Salmon said two other firefighters were in critical condition.He said the dead firefighters were Paul Cahill and Warren Payne, who served on Engine 30, Ladder 25, the first to respond to the fire Wednesday evening.Salmon said eight other firefighters had less serious injuries, and an EMS paramedic was being evaluated for chest pains.The four-alarm fire started at about 9 p.m. in the Tai-Ho Mandarin and Cantonese restaurant and spread to an adjoining building in a one-story row of yellow-brick storefronts, where at least three other stores were damaged. The fire was put out within about an hour.Boston Fire Chief Kevin MacCurtain said the most seriously injured were members of the first crew that responded to the fire. They were trapped after they became disoriented in heavy smoke.Associated Press material was used in this report.