A United Steelworkers of America report suggests a fire that led to an explosion last May at Pacific Engineering and Production Co. started in a batch dryer, instead of from a spark from a welder's torch.

The report released Thursday said although the dryer was responsible for several fires prior to May 4, 1988, Pacific Engineering officials failed to modify equipment or install adequate fire suppression systems.The union study contradicts an investigation by the Clark County Fire Department, which concluded a spark from a welders' torch ignited the fire, which then ignited ammonium perchlorate produced and stored at the plant.

The resulting blasts killed two plant workers, injured 350 residents and caused an estimated $74 million in damage throughout the Las Vegas Valley.

Ammonium perchlorate is an oxidizing agent used in solid fuel rockets and missiles. It is critical to the nation's defense and space programs.

Pacific Engineering has since selected a new plant site near Cedar City, Utah, where the facility is currently under construction. The facility is scheduled for completion this summer.