A buried grease interceptor fits OSHA's definition of a confined space: a person can climb in, the way out is restricted, and it is not built to be occupied. Decaying grease can leave toxic gas inside, so entry needs air testing, ventilation, an attendant at the opening and rescue gear. That takes a crew, not one person.
Is a grease interceptor a confined space?
Yes, in the ordinary case. OSHA defines a confined space by three tests. It is a space that "Is large enough and so configured that an employee can bodily enter and perform assigned work," that "Has limited or restricted means for entry or exit," and that "Is not designed for continuous employee occupancy." The definition lists "tanks, vessels, silos, storage bins, hoppers, vaults, and pits" as examples of spaces that may have limited means of entry. A multi-chamber interceptor tank reached through a manway meets all three.
Some very small hydromechanical traps under a sink do not. Nobody climbs into those. This page is about the outdoor gravity tanks that restaurants, commissaries and food courts use.
What makes it a permit-required space?
A confined space becomes a permit space when it has one or more of four characteristics. Two matter for an interceptor: it "Contains or has a potential to contain a hazardous atmosphere," and it can contain "a material that has the potential for engulfing an entrant."
The gas is the usual culprit. Food waste and grease decay in the tank and produce hydrogen sulfide. OSHA's hazard page lists the general industry ceiling limit at 20 ppm and the NIOSH immediately-dangerous level at 100 ppm. At 100 ppm it lists "loss of smell after 2-15 minutes (olfactory fatigue)." That is the trap: the rotten-egg smell you can notice at low levels stops warning you at the levels that hurt. Our page on why concrete interceptors corrode covers how the gas forms, and sewer gas limits at work covers the exposure numbers.
OSHA also counts oxygen. A "hazardous atmosphere" includes "Atmospheric oxygen concentration below 19.5 percent or above 23.5 percent." A closed tank that has been sitting can be short on oxygen with no smell at all.
Which OSHA rule applies to an interceptor repair?
Two rule sets cover confined spaces, and which one governs depends on the work. The general industry standard, 1910.146, "does not apply to agriculture, to construction, or to shipyard employment." OSHA defines construction work as "work for construction, alteration, and/or repair, including painting and decorating." Construction confined-space work falls under Subpart AA, starting at 1926.1203, and its introductory note lists "precast concrete and other pre-formed manhole units," "sewers" and "lift stations" among places where confined spaces occur.
Rather than guess which one a particular visit falls under, the employer doing the entry runs a written program that meets the applicable rule. The roles and the steps are nearly the same in both. We cover the owner's side of that question for private manholes in who coordinates entry into a private sewer manhole.
Who stands where on the crew?
The rules assign three jobs. They are different people's jobs for a reason: the person inside cannot watch their own air.
| Role | What OSHA says the job is |
|---|---|
| Authorized entrant | Goes in. Must "Alert the attendant whenever" there is "any warning sign or symptom of exposure to a dangerous situation," and must exit as quickly as possible when ordered or when a prohibited condition shows up. |
| Attendant | Is "stationed outside" the space, "Continuously maintains an accurate count of authorized entrants," and "Performs no duties that might interfere with the attendant's primary duty to assess and protect the authorized entrants." |
| Entry supervisor | "Verifies, by checking that the appropriate entries have been made on the permit, that all tests specified by the permit have been conducted" before endorsing the permit, and "Verifies that rescue services are available." |
The general industry rule requires "at least one attendant outside the permit space into which entry is authorized for the duration of entry operations." It also says an entry supervisor "also may serve as an attendant or as an authorized entrant, as long as that person is trained and equipped as required." So the minimum on paper can be smaller than three. HQ staffs its grease interceptor repair and inspection work with a three-person confined-space crew, which keeps the three jobs on three people and leaves the attendant free to do the one thing that job exists for.
What has to happen before anyone goes in?
The order matters. For the pared-down procedure OSHA allows when ventilation alone controls the hazard, the construction rule says "Any conditions making it unsafe to remove an entrance cover must be eliminated before the cover is removed," and then "When entrance covers are removed, the opening must be immediately guarded by a railing, temporary cover, or other temporary barrier that will prevent an accidental fall through the opening." Next the air is tested "for oxygen content, for flammable gases and vapors, and for potential toxic air contaminants, in that order." The rule adds that "Continuous forced air ventilation must be used" and that no one enters until it has "eliminated any hazardous atmosphere." A tank with liquid and sludge in it has more than an air problem, so the full permit program, with its attendant, supervisor and rescue plan, is the usual path.
Rescue is planned before entry, not after. Under the construction rule, "Non-entry rescue is required unless the retrieval equipment would increase the overall risk of entry or would not contribute to the rescue of the entrant." That means a chest or full-body harness and a retrieval line, and "A mechanical device must be available to retrieve personnel from vertical type permit spaces more than 5 feet (1.52 meters) deep." That is the tripod and winch you see over an open interceptor. Nobody is supposed to climb in after a person who collapses.
The tank also has to be pumped empty first, by a licensed hauler. Our page on the order of pumping and repair walks through that.
Does looking inside count as entering?
Many people underestimate how little it takes. OSHA's definition says "Entry" is "considered to have occurred as soon as any part of the entrant's body breaks the plane of an opening into the space." Putting your head and shoulders into the manway to see the baffles counts. Looking in from outside with a light, a camera on a pole or a mirror does not, which is why a lot of first-pass interceptor inspections are done from the surface.
What should the restaurant owner do?
Stay out of the opening and keep staff away from it while the crew works. Phoenix's FOG manual tells operators to witness the cleaning "to ensure the pumping company is completely cleaning the interceptor," and says it is "a good time to inspect for damaged or missing parts." Do that from beside the manway, not from the ladder.
If you hire a contractor for the entry, the host employer's duties include informing "the contractor that the workplace contains permit spaces" and apprising "the contractor of the elements, including the hazards identified and the host employer's experience with the space." Tell the crew about prior odors, past incidents, a dishwasher discharging into the tank or any change to what flows in. Parking and drive-thru lanes matter too, because a lid in traffic needs the area blocked off, a topic we cover in grease interceptor lids and covers.
HQ repairs and inspects grease interceptors, including baffles and inlet and outlet fittings, but does not pump them. A separately licensed hauler empties the tank first. We give free estimates and upfront pricing before the work starts.