Septic Tank Safety: Lids, Gases and Collapse Risks

The three main dangers of a septic tank are the gases inside it, an open or weak lid someone can fall through, and an old tank that can collapse. No one should ever enter a septic tank. Keep the lids secured so children can't open them, keep vehicles off the tank, and have a septic company look at any lid or ground that is cracked, sinking or caving in. A tank that is no longer used has to be abandoned properly, under a permit.

If someone has fallen into a tank or collapsed next to one, call 911 now and don't go in after them.

What is in the air inside a septic tank

"Even properly operating septic tanks contain poisonous gases," says NC State Extension's septic owner's guide, which also warns that "toxic and explosive gases in the tank present a hazard." The gases to know about:

Hydrogen sulfide. OSHA describes it as a colorless gas with a rotten egg smell at low levels. It is heavier than air, extremely flammable and highly toxic, and it occurs naturally in sewers. OSHA warns that after a while, or quickly at high levels, you can no longer smell it, so the smell is not a reliable warning. At high enough levels, OSHA lists collapse within 1 to 2 breaths.
Methane. The Wisconsin Department of Health Services says high methane levels in enclosed spaces can lower oxygen enough to cause unconsciousness and death, and that methane and hydrogen sulfide are both flammable and highly explosive.
Too little oxygen. Wisconsin DHS says high concentrations of methane in enclosed areas decrease the amount of oxygen in the air and can cause suffocation, and OSHA lists low oxygen among the hazards of sewer confined spaces.

Because these gases are flammable, keep flames and sparks away from an open tank. NC State Extension also warns that electrical controls present a shock and spark hazard.

Never enter a tank, even to help someone

OSHA defines a confined space as one large enough to enter, with limited ways in or out, and not designed for continuous occupancy. A septic tank fits that description. OSHA lists low oxygen and toxic or flammable gases among the hazards of sewer confined spaces, and warns that rescue attempts by untrained people can lead to multiple deaths. A 1986 NIOSH alert on workplace confined-space deaths noted that 60% of deaths in confined spaces involve potential rescuers. In one case NIOSH investigated that year, four employees of a septic tank service company were overcome by toxic fumes in an industrial septic tank, and three of them died.

If someone goes down at an open tank:

Call 911 and say it is a confined space with possible toxic gas.
Stay out of the tank and keep everyone else out too.
Keep children and pets away from the area.

The EPA says only trained specialists should clean or repair septic tanks, because tanks may contain dangerous gases. Pumping, inspections and repairs are jobs for a septic company. Our guide to what happens during a pump-out explains how a crew works from the surface.

Lids and risers: what Florida's rule requires

Florida's standard for septic tanks, Rule 62-6.013, F.A.C., says access manholes must be made "vandal, tamper, and child resistant." It accepts one or more of these methods, as specified by the tank maker:

A padlock.
A twist lock cover requiring special tools for removal.
Covers weighing 58 pounds or more, net weight.
A hinge and hasp with stainless steel or other corrosion-resistant fasteners, for fiberglass, metal or plastic lids.

The same rule says the access manholes over the inlet and outlet must extend to within 8 inches of finished grade, that a riser must be closed by a riser access lid or manhole cover, and that risers must be watertight. These are construction standards for tanks, and an older tank may have been installed under earlier rules. If you are not sure your lids are secure, ask your septic company at the next visit.

After a pump-out, Rule 62-6.010 says the original lid must be put back in place, or replaced with a new lid if it is broken, and the lid must be completely sealed and secured. It is worth checking the lids yourself after any service visit. Look at them from beside them; don't stand on a lid or lift it.

NC State Extension recommends risers on tanks buried 6 inches or deeper, because they make pumping and filter cleaning easier, and says to make sure a riser is secured with a lock or a heavy lid so children can't open it. Published ranges put risers at about $100–$400 and a tank lid replacement at about $150–$600. Replacing a broken lid alone is not counted as a repair under Rule 62-6.002, F.A.C.

Signs a tank may be failing or collapsing

NC State Extension says plainly: "Old tanks may collapse." The Washington State Department of Health adds that people do accidentally fall into septic tanks, and says to inspect lids routinely and repair or replace damaged or missing parts. Watch for these signs:

What you see	Why it matters
A cracked, broken, rusted or missing lid	Someone could fall in (Washington State DOH)
Ground settling or sinking over the tank	The EPA lists settling as a sign of damage after a flood
Cars or equipment driven over the tank	Florida DOH in Columbia County warns that driving over a tank can crack or break its lid
Flooded or saturated ground around the tank	The CDC says a septic tank can collapse or float out of position in a flood

If you see any of these, keep people, pets and vehicles away from the spot and call a septic company. Don't try to lift or probe a damaged lid. In flooded conditions, don't have the tank pumped: Florida DOH warns that a very high water table can make the ground cave into a tank that was pumped dry.

Protect the tank day to day. The Columbia County health department says not to let vehicles drive over any part of your septic system, and the EPA says not to park or drive on your drain field.

Old and abandoned tanks

Florida law requires a permit to abandon a septic system (s. 381.0065(4), F.S.). Under Rule 62-6.011, F.A.C., when a home connects to sewer, or an old tank is replaced with a new one, the old system must be abandoned within 90 days and can't be used for any other purpose. (The rule has narrow exceptions, such as a tank approved for reuse as part of a permitted wastewater or stormwater system.)

The rule sets out how abandonment is done under a general permit:

The contractor files a notice of intent with DEP and pays the fee. DEP issues the general permit, which is valid for 18 months.
A permitted septage company pumps out the tank and gives a receipt, unless the tank is already empty and dry.
The bottom of the tank is opened or ruptured, or the whole tank is collapsed, so it can't hold water.
The tank is filled with clean sand or other suitable material and completely covered with soil. If it can't be ruptured or collapsed, it is filled with flowable fill concrete. As an alternative, the tank can be removed from the site and scrapped.
The contractor certifies the work and sends DEP the pump-out receipt and dated, located photos of the emptied tank, the fill and the finished site.

The rule also allows abandonment under a system construction permit. If you find a tank on your property that you didn't know about, or you suspect an old tank was never properly abandoned, keep people off the area and contact your county health department (or Florida DEP in Marion County). Our county septic permit offices page lists who to call. If you are connecting to sewer, our septic vs. sewer guide covers Florida's connection rules.

Children and pets

Never leave an open lid unattended when the system is being inspected or pumped, and teach children that tank lids are not to be played on or opened (Washington State DOH).
Make sure lids are back on and secure when work is finished (Washington State DOH; Rule 62-6.010).
Secure risers with a lock or a heavy lid so children can't open them (NC State Extension).
Keep children and pets away from any sewage on the ground or in the house. Our sewage backup guide covers cleanup.

A short safety checklist

Know where your tank and lids are. The EPA says the local permitting authority may have a record drawing of your system.
Check that each lid is intact and secured, especially after a pump-out. Look from beside the lid; don't stand on it or lift it.
Keep cars, trailers and heavy equipment off the tank and drain field.
Report cracked lids, settling ground or a strong sewage smell in the yard to a septic company.
Never open, enter or lean into the tank. Leave it to professionals.
Check a company's Florida DEP registration with our registration checker before hiring.

Frequently asked questions

Can I open my own septic tank lid?

It is safer not to. The EPA says only trained specialists should clean or repair septic tanks, because of the gases inside, and an old lid may be weak. NC State Extension says never to enter a septic tank.

Is the sewage smell in my yard dangerous?

A rotten egg smell can mean hydrogen sulfide. OSHA says prolonged exposure even at low levels may cause nausea, tearing of the eyes and headaches, and that you can stop smelling it, quickly at higher levels. Don't go near an open tank, and have a septic company find the source. See the signs of a full or failing tank.

Do I need a permit to replace a broken lid?

Replacing a broken lid on its own is not a repair under Rule 62-6.002, F.A.C. Ask the company whether any other work it finds needs a permit.

Who can abandon an old septic tank?

Under Rule 62-6.011, the contractor doing the abandonment files the notice of intent, and a permitted septage company pumps the tank. Ask your county health department, or DEP in Marion County, how it handles abandonment permits.

What should I do if a child or pet falls into a tank?

Call 911 right away and say it is a septic tank. Don't climb in: OSHA warns that untrained rescuers can die too.