An Open Septic Tank Can Kill, and So Can a Rescue Attempt

A septic tank is a confined space: hard to get into and out of, never meant for a person to stay in, and able to hold gases that can drop someone where they stand. On a rural lot the tank usually sits quietly under the yard, which makes it easy to forget what is inside.

Why is the gas so dangerous?

Because the warning sign disappears. Hydrogen sulfide, the gas most people call sewer gas, smells like rotten eggs at first. Federal health officials at ATSDR say people lose the ability to smell it after about 2 to 15 minutes at around 100 parts per million, which makes the odor useless as a warning, and that above 100 ppm people can lose their sense of smell or lose consciousness. At concentrations over 150 ppm it can cause lasting harm or death (ATSDR).

OSHA's definition fits a septic tank exactly. It describes confined spaces as places with limited ways in and out, not designed for continuous occupancy, and names tanks, pits, vaults and manholes as examples; a space that holds, or could hold, a hazardous atmosphere is classed as permit-required (OSHA, archived copy).

Why must no one go in after a person who collapses?

Because the same air will take the rescuer too. In a 1986 case investigated by NIOSH, a septic service worker went into a 2,000-gallon waste tank after it was pumped and was overcome. A second, third and fourth worker went in to help, one after another. Three of the four died (NIOSH FACE 86-38). That tank was at a hatchery, not a home, but the gas behaves the same way.

If someone is down in or beside a tank, call 911, keep everyone else back, and tell the dispatcher it is a septic tank. Wait for trained responders.

What homeowners can and can't do

You can keep the lids and risers closed and secured, mark where the tank is, and keep children and dogs away from open access points while a pumper is working. You should not open the tank, lean over an open riser, put your head or arm into it, or climb into the excavation around it. Opening, pumping and repairs are work for a county-permitted pumper or a licensed C-42 contractor; see septic pumping and inspection and septic trouble signs. The same caution applies to water storage tanks, covered in water storage tanks.

Sources

1. ATSDR (CDC) — ToxFAQs: Hydrogen Sulfide — loss of smell, unconsciousness and death thresholds
2. NIOSH — FACE 86-38, Three Dead, One Critical in Industrial Septic Tank in Georgia — rescuers overcome one after another
3. OSHA — Confined Spaces overview (archived copy) — definition of confined and permit-required spaces