Here in the United States, OSHA establishes the requirements for "permit-required confined spaces". The federal regulation 29-CFR-1910.146 covers this. This regulation is for general industry and contains procedures to protect employees in general industry from the hazards of entering confined spaces. Note that this regulation does NOT pertain to construction.
OSHA's construction safety and Health regulations Part 1926 covering construction safety issues does not include a permit-required confined space requirement. However it does specify certain safety training and education requirements for people who are required to enter confined spaces.
I mention the above just to clarify that entry rules are different for contractors and owners. The rest of this message deals with permit required confined space classification for general industry.
First, let's review some basic definitions. A confined space needs to satisfy the following three criteria (per OSHA):
1. large enough to enter and perform work.
2. has limited or restricted means for entry or exit.
3. is not designed for continuous occupancy.
First off, if it's not a confined spece, it can't be a "permit-required" confined space. We've intentionally overdesigned metering and sampling VAULTs with ventilation fans, actual stairs and spring loaded, full size Bilco doors in order to eliminate the LIMITED OR RESTRICTED MEANS FOR ENTRY OR EXIT criteria. Yes, it's more expensive to build but for vaults that must be entered regularly, it's well worth the additional cost not to have to contend with a confined space.
Next, once you have a space that's classified a confined space, you really have to start with the worst possible scenereo and prove your way backward. That basically says that all confined spaces are "permit required" confined spaces until proven otherwise. OSHA's permit required criteria stresses the existence of a hazardous or potentially hazardous atmosphere. But it also has a catch-all statement "a space that contains any other serious safety or health hazard". So if you have a confined space, it's difficult to classify it as anything other than "Permit-Required". Water system meter and valve vaults are included here.
Let me give you an example. About 30 years ago, we were involved in supervision of the construction of a pipeline. This was a new sewage force main that had never had anything in it, and had not even been pressure tested. On that force main was a manhole and in the manhole was a tee with the side outlet flanged off. This tee was provided to allow future access to the force main. The pipeline and manholes had been constructed without incident. One day a two-man crew was going around grouting the inside of the manholes. Worker A enters the manhole. Worker B goes over to the manhole and sees Worker A laying at the bottom of the ladder. He figures worker A slipped and fell off the manhole ladder. So worker B goes in after him. Supervisor sees both workers at the bottom of the manhole and calls the fire department. Both workers died in a manhole which was completely sealed from the pipeline that had never had anything in it. It was determined to be oxygen deficiency but nobody ever determined the cause.
With a permit-required confined space, OSHA allows what is called "Alternate Entry", which lets you enter a space using permanent or portable forced air ventilation alone if you can show that the only hazard posed by the space is a potential hazardous atmosphere. You can enter as long as the space is ventilated and monitored, but you don't have to comply with the "permit" requirements of having an attendant, a safety harness and a rescue team on notice. This alternate entry procedure is for that one event only. You still need to fill out an entry form documenting the entry event and the fact that it was done on "alternate entry".
Sorry this is so long winded. I hope it helps. Be safe.
