The director of the OSHA office investigating the accident that killed four workers in a sewer at a Superior, Wis., landfill last Thursday says it may take months before their work is complete, according to the Associated Press.

Area director Mark Hysell says one of the things they'll look at is whether the company that owns the property was required to have specific procedures for entering confined spaces. The permit procedures define what needs to be done when entering such a space.

Asked about the company's safety record, Hysell says OSHA has never inspected the company for workplace safety.

Authorities say one of the workers was trying to repair a pump or clear a blockage in the sewer line when he was overcome by fatal fumes and the others went down into the hole to attempt a rescue.

The four are believed to have died from toxic fumes while trying to fix the sewer in a hole about three feet in diameter and at least 12 feet deep. Experts said the level of deadly hydrogen sulfide fumes was so high it would have immediately knocked each worker unconscious.

The property owner said the landfill is for demolition products, as when buildings are torn down, and the pit acts as a collection tank for drainage and leeches water before it is pumped into the city sewer system.