Different types of confined spaces exist, and some of them pose dangers that necessarily require the use of a permit. A confined space, according to OSHA 29 CFR 1910.146 “Permit-required confined spaces”, is a space that is sufficiently large and configured to enable an individual to access in full body to execute project tasks, the point of entry and/or exit is limited or constrained, as in the case of a vessel or tank, and the space was not constructed for employee occupancy for an extended period of time.

The main risks of entering a permit-required confined space can be described, according to OSHA, as follows:

• Exposure to hazardous atmosphere.
• Exposure to materials with potential for engulfing.
• Possible entrapment or asphyxiation.

OSHA's 1910.146 standard lists certain preventative steps that apply to both the primary employer and any contractor doing asset inspections, including but not limited to:

• Pre-entry hazard evaluations.
• Specification of acceptable entry conditions.
• Verification of the conditions as acceptable.
• Coordination of entry operations.
• Isolation of the confined space.
• Usage of forced ventilation.
• Purging, inerting, flushing, or ventilating the permit space as necessary to eliminate or control atmospheric hazards.
• Provision of personal protective equipment, lightning equipment and communication equipment for the person entering the confined space.