MENOMINEE, Mich. (AP) _ Methane gas killed a dairy farm owner and four other men after one slipped into a manure pit and the others tried to rescue him.

The victims included owner Carl Theurkauf Sr., his son Carl Jr. and his grandson Danny, said a relative who would not give his name. Identities of the other two were not released immediately.

''It was my father and my brother, and I don't really feel like talking about it right now,'' the man said.

Officers were called to the farm in the southwestern corner of Michigan's Upper Peninsula shortly before 9 a.m. Wednesday, said Deputy Gary Corwin of the Menominee County Sheriff's Department.

The accident occurred in an uncovered, concrete-lined pit with one sloping side allowing waste to slide to the bottom.

''It appeared they were cleaning it and the first victim just happened to slip ... down the incline plane; a second went down and was overcome also,'' said Dr. Paul Haupt, county medical examiner. ''Then another went down to get the other two, and so on and so on.''

The victims probably were overcome within 90 seconds of exposure to methane, an odorless gas generated by the animal waste in the pit, Haupt said. No autopsies were planned.

''It's been really hot up here, and they were in the pit with about a foot of cow sewage,'' he said. ''The gas was forming and just sort of sitting there on top of the liquid. It was displacing the oxygen ... like being on the moon.''

The victims ranged in age from 18 to 60, Corwin said. One man was dead when police arrived.

Three others died later Wednesday at Bay Area Medical Center in Marinette, Wis., and the fifth at Children's Hospital of Wisconsin in Wauwatosa, Wis., he said.

Haupt said other dairy farmers told him that uncovered pits are common.

''It's a known hazard, and why they're not covered, I don't know,'' he said.