A few months ago I addressed some safety concerns for onsite system service providers and inspectors. As I continue to travel around the country to speak to wastewater professionals, I hear from contractors who talk about the need to enter tanks to complete repairs to baffles and other components.

At the same time, not a year goes by without reading or hearing about someone dying when entering a septic tank without adequate confined-space training or equipment. Sadly, very often there are multiple fatalities in these cases as someone enters the tank in an attempt to save the person overcome by dangerous fumes.

Any enclosed working area faced by onsite professionals should be considered dangerous, but the confined space most associated with septic service technicians is the septic tank. By definition, a confined space is an area with limited entry and exit that contains known or potential hazards, has poor natural ventilation, and is not designed for continuous human occupancy.

Deep excavations to access septic tanks or pump tanks present some of the same confined-space hazards in addition to the potential for collapse of the excavation. Worker safety laws require special precautions, equipment and training for entry into confined spaces.

THREAT OF TOXIC GAS

When faced with a confined-space situation, three primary sources of concern come to mind: oxygen deficiency, toxic gases and explosive conditions. Suffocation caused by oxygen deficiency is due to the biological and chemical activity in the tank consuming oxygen. In addition, the percentage of oxygen in the air is reduced due to the formation of gases such as carbon dioxide and methane.

The atmosphere contains 21 percent oxygen. At 14 to 16 percent, the safe exposure limit is eight hours. For a short time humans can tolerate levels as low as 12 percent. At 7 percent the condition is fatal. An oxygen deficiency meter should be used to determine if levels are sufficient.

Toxic gases that are common in septic tanks and other system components are hydrogen sulfide and carbon dioxide. They are both formed during anaerobic decomposition occurring in the septic tank. Hydrogen sulfide can be detected by the distinctive rotten egg odor; the problem is that the sense of smell is lost quickly as the concentration of the gas increases. Hydrogen sulfide gas can be detected by a hydrogen sulfide detector or lead acetate paper.

Carbon dioxide, on the other hand, is an odorless and colorless gas. It is heavier than air so will be found at the bottom of the tank. In general, if oxygen levels are sufficient it usually means that carbon dioxide will be in the safe range.

NO SMOKING

The most common explosive agent found is methane. Methane is colorless and odorless and is not toxic but can cause oxygen depletion. It is explosive at concentrations of 5 to 15 percent. Everyone has a story about an explosion triggered by someone smoking around the tank while pumping. That is a good reason service providers should not smoke while pumping a tank. Recognize the risk of explosion and refrain from using electrical tools or any items with sparks or flames until the situation is safe.

A confined space must be adequately ventilated using blowers and large-diameter flexible hose before worker entry. The person entering the space should be secured with a lifeline attached to a safety harness. Appropriate lifeline materials are 3/4-inch manila, 1/2-inch nylon or 1/2-inch polypropylene. Two physically able people should remain on the surface when someone enters a tank.

The confined-space rescue of a person not wearing a lifeline should only be undertaken by someone wearing a self-contained breathing apparatus and a lifeline, or after proper ventilation of the space. Generally two fatalities occur when someone enters the tank to save a worker without following these guidelines. Make sure this does not happen to you!

Confined-space training programs are available through state worker safety offices. If you frequently encounter confined-space situations or deep excavations, make sure your entire crew has the proper training and that all necessary safety equipment is available.