4.2 Confined spaces, including the ones you create yourself

1 The paragraph that makes it your problem

1910.146(c)(6) is one sentence: "When there are changes in the use or configuration of a non-permit confined space that might increase the hazards to entrants, the employer shall reevaluate that space and, if necessary, reclassify it as a permit-required confined space."

Changes in use or configuration. A maintenance job is often both. Hot work introduces an ignition source and a fume source that were not in the space yesterday. A solvent wash introduces a flammable vapor and a toxic one. An inert purge removes the oxygen. Cutting an opening changes the ventilation. Running a hose in changes the atmosphere and adds an engulfment risk. Every one of those is a change in use that "might increase the hazards to entrants," and the reevaluation is owed before the entry, not after somebody feels dizzy.

The reverse direction has a paragraph too, and it is stricter than people expect. (c)(7)(i): a permit space may be reclassified as a non-permit space only "if the permit space poses no actual or potential atmospheric hazards and if all hazards within the space are eliminated without entry into the space" — and only "for as long as the non-atmospheric hazards remain eliminated." (c)(7)(ii): if entry is needed to eliminate the hazards, that entry is a full permit entry under paragraphs (d) through (k).

2 Alternate procedures: six conditions, then eight requirements

1910.146(c)(5) is the middle path, and it is the one most maintenance entries in a clean plant actually use. It lets an employer skip paragraphs (d) through (f) and (h) through (k) — the full permit program, the attendant, the rescue service — but only under conditions the employer must be able to demonstrate. (c)(5)(i): the only hazard posed by the space is an actual or potential hazardous atmosphere; continuous forced air ventilation alone is sufficient to maintain the space safe for entry; the employer develops monitoring and inspection data supporting both of those demonstrations; any initial entry needed to obtain that data is performed as a full permit entry; the determinations and data are documented and made available to each employee who enters; and the entry is performed in accordance with (c)(5)(ii).

Then (c)(5)(ii) sets out what the entry looks like, and the eight items are worth knowing because they are what a good maintenance entry does anyway.

• (A) Any conditions making it unsafe to remove an entrance cover shall be eliminated before the cover is removed. A pressurized or hot manway is a hazard before it is an opening.
• (B) When covers are removed, the opening "shall be promptly guarded by a railing, temporary cover, or other temporary barrier" that prevents an accidental fall through and protects the person inside from foreign objects entering.
• (C) Before entry, the internal atmosphere is tested with a calibrated direct-reading instrument "for oxygen content, for flammable gases and vapors, and for potential toxic air contaminants, in that order," and any employee entering may observe the pre-entry testing.
• (D) There may be no hazardous atmosphere within the space whenever any employee is inside it.
• (E) Continuous forced air ventilation is used: nobody enters until the ventilation has eliminated any hazardous atmosphere; the air is directed to ventilate the immediate areas where employees are or will be; it continues until all employees have left; and the supply is from a clean source that does not increase the hazards in the space.
• (F) The atmosphere is periodically tested as necessary to ensure the ventilation is preventing accumulation, and entrants may observe the periodic testing.
• (G) If a hazardous atmosphere is detected during entry: everyone leaves immediately, the space is evaluated to determine how the atmosphere developed, and measures are implemented before any subsequent entry.
• (H) The employer verifies the space is safe for entry and that the pre-entry measures have been taken "through a written certification that contains the date, the location of the space, and the signature of the person providing the certification," made before entry and available to each entrant.

Item (C)'s order is not decorative: oxygen first, because a combustible gas sensor's reading depends on oxygen, then flammables, then toxics. Item (E)'s clean source clause is the one that catches a crew that puts a blower inlet next to a running engine or a paint booth exhaust.

3 Isolation is the same problem you solved in Part 2

A vessel that is drained is not a vessel that is isolated. Product arrives through the line you did not blind, a level control opens a valve on a signal nobody expected, an agitator has its own feed, and a nitrogen blanket keeps arriving because the blanket system is doing its job. Everything in Part 2 applies, with two additions that vessels make sharper.

First, for fluids the isolation device that satisfies 1910.147(b) may need to be a blind rather than a valve — the definition of a lockout device explicitly includes "blank flanges and bolted slip blinds." A closed and locked valve is an isolation; a valve that can leak past its seat into a space with a person in it is a different risk calculation than the same valve on a pump you are rebuilding.

Second, agitators, screws, rakes and paddles inside a vessel are the mechanical hazard that (c)(7)(i) is talking about when it says "all hazards within the space are eliminated." A locked disconnect handles energization. A pinned or removed drive coupling handles the rest, and it is what turns a mechanical hazard from controlled into eliminated.

4 Host and contractor: the five-and-three duty

Maintenance work in confined spaces is contracted more often than any other kind, and 1910.146(c)(8) and (c)(9) split the duty explicitly. When a host employer arranges to have another employer's employees perform work involving permit space entry, the host shall: inform the contractor that the workplace contains permit spaces and that entry is allowed only through compliance with a permit space program meeting the section; apprise the contractor of the elements, "including the hazards identified and the host employer's experience with the space," that make it a permit space; apprise the contractor of any precautions or procedures the host has implemented for protection of employees in or near those spaces; coordinate entry operations when both host and contractor personnel will be working in or near permit spaces; and "debrief the contractor at the conclusion of the entry operations regarding the permit space program followed and regarding any hazards confronted or created in permit spaces during entry operations."

The contractor's three duties in (c)(9) mirror them: obtain the available information about hazards and entry operations from the host, coordinate entry operations with the host, and inform the host of the program the contractor will follow and of any hazards confronted or created — "either through a debriefing or during the entry operation."

"Hazards created" is the phrase to notice. Both paragraphs assume the entry itself will produce hazards that did not exist before, and both require them to be reported. That is the confined space version of the same idea as management of change in Part 5, Chapter 4.

5 A cleaning job in a tank

On January 30, 2025, an employee at a trailer truck wash business — a business that specialized in washing out livestock haulers — had been subcontracted to clean out a trailer tank with a water hose. He entered the tank to continue cleaning. A coworker later noticed him lying on his side in the bottom of the tank; the local fire department retrieved him and he died of head injuries (OSHA Accident Summary Nr 173951.015). The keywords OSHA attached include Cleaning, Confined Space, Fall, Fall From Elevation, Fall Protection, Hose, Multi-employer Worksite and Tank Cleaning.

Take the list apart and every element of this chapter is in it. A cleaning task — servicing under 1910.147(b). A tank — a space whose hazards changed when water and a hose went in. A wet interior — a fall hazard created by the work. A subcontracted crew — the multi-employer coordination of (c)(8) and (c)(9). And an entrant found by a coworker rather than watched by an attendant.

6 What to do with all of this on a Tuesday

Most maintenance technicians will never be the entry supervisor and should never be the entrant on an atmosphere they have not seen measured. What they can do is recognize when a job has crossed a line, and stop it there.

1. 1
   Name the space before you plan the job. Is it a confined space at all, is it a permit space, and who decided? 1910.146(c)(1) puts the evaluation on the employer, and (c)(2) requires permit spaces to be identified by danger signs or an equally effective means.
2. 2
   Ask what your work adds. Hot work, solvent, purge gas, a new opening, water, a hose — each is a change in use or configuration under (c)(6), and each one may reclassify the space.
3. 3
   Do not accept ventilation as elimination. The Note to (c)(7) is explicit, and the difference decides whether you need a permit program or the alternate procedures of (c)(5).
4. 4
   Insist on the reading, in the right order, from a calibrated direct-reading instrument — oxygen, flammables, toxics — and know that (c)(5)(ii)(C) gives you the right to watch it being taken.
5. 5
   Isolate like Part 2 taught you, and then ask what would eliminate rather than control: a blind instead of a valve, a coupling removed instead of a disconnect locked.
6. 6
   If you are the contractor, get the host's information before you mobilize, and give them yours. If you are the host, debrief the contractor at the end — both are requirements, not courtesies.

The full treatment of permit spaces — the permit itself, the attendant, the entry supervisor, rescue and the atmospheric numbers — is the subject of the Confined Space Awareness course on this site. This chapter covers only the part that belongs to maintenance: the fact that your work is often what makes the space dangerous.