Last week's farm accident near Bridgewater, Va., claimed the lives of Mennonite farmer Scott Showalter, his wife Phyllis, two of their four children and an employee. News headlines across the country claimed "Methane gas kills five".

But the details of the tragic event suggest that methane gas from the farm's manure pit probably wasn't the cause. But without an autopsy, the exact cause may never be known, says out Dennis Murphy, ag safety specialist at Penn State University.

Showalter was transferring manure from a pit under his dairy barn to a holding pond. This time, something had clogged the drain, and the Rockingham County farmer went in to unclog it. Authorities say he was quickly overcome.

Immediately, the employee went in to rescue him and also passed out. Another employee alerted Mrs. Showalter who rushed to the pit with daughters Shayla and Christina. All three fell victim to toxic gases.

The most likely killer was...

"They were moving manure, and that's when you get high concentrations of hydrogen sulfide, a highly toxic manure gas," points out Murphy. "At low concentrations, it has a rotten egg smell – but not at high concentrations!"

At high levels, the gas will paralyze the sense of smell, according to a Center for Disease Control report from the National Ag Safety Database. A Cornell safety fact sheet updated this winter confirmed that high concentrations – 800 parts per million or higher of hydrogen sulfide can cause rapid loss of consciousness, diaphragm paralysis at first breath and asphyxiation.

Safety advice

Any time you work with a manure pit, there's a high degree of danger, warns Murphy. "They're more deadly than you realize." Here are a few of his suggestions:

Always assume hydrogen sulfide is present. It's heavier than air and hangs in low-lying, unventilated areas. Because of that, levels may remain high in some confined places even with ventilation.

Provide extra ventilation during agitation and before going into any pit.

Never enter a pit without precautions and a backup emergency plan. That plan should include a trained co-worker stationed outside the pit in case of emergency.

As cumbersome as it might be, wear a safety harness or belt with a lifeline secured outside the storage area. Be sure the trained back-up person can life the person inside to safety with a winch or pulley if necessary.

You'll find much manure storage safety information on the Web. Here are two sites to start with:

Manure storage poses invisible risks: www.phppo.cdc.gov/nasd/docs.  

Hydrogen sulfide in manure handling systems: www.manuremanagement.cornell.edu.