TERRE HAUTE, Ind.—tprp—A task force headed by fire and gas explosion experts today probed for the cause of the meat packing plant explosion here that killed 16 men. “It looks like everything blew from the bottom up and every thing caved in,” said Ray Mc Manus, assistant fire chief here. Rescue workers combed the debris of the 54-year-old two story brick building which had housed the Home Packing Co. for 28 hours before they pulled the last victim from the rubble. Three of 58 men _ injured re mained in critical condition. McManus said although “there was some talk of an ammonia gas explosion” at the refriger ated plant, “we are discounting it and concentrating on the na tural gas angle.” The investigation began late Thursday with officials from city and state fire departments, police, and insurance men wear ing gas masks to ward off the still swirling clouds of the dead ly ammonia gas. Robert F. Scott, president of the packing company, indicated the answer will be found in the basement, when the huge amounts of debris and ammonia gas are cleared away. Damage to the plant was estimated at $750,000. An expert on gas explosions, Wilbur Walls of the National Fire Life Insurace Co., was expected to arrive here today. Bernard Sweeney, chhef in vstigator for the Indiana fire marshal's office, impounded the length of gas pipe where leaks were first discovered and sent it to the Indiana State Police Laboratories. Scott said reports that a boil er had blown up have proven untrue. He said there was a con siderable amount of natural gas escaping in the area. Gas com pany men have cut off all mains leading into the area. Scott said, “I imagine it will be a matter of days” before the cause of the blast is determined.