Acceptable Limits

DOE-EM-STD-5503-94

on to ensure the contaminants are removed and that the ventilation system is not causing a

hazardous condition.

13.9.3. Acceptable Limits

The atmosphere of the confined spaces should be considered within acceptable limits whenever

the following conditions are maintained:

Oxygen - 19.5% to 23.5%,

Flammability - less than 10% of the Lower Flammable Limit (LFL), and

Toxicity - less than recognized ACGIH exposure limits or other published exposure

levels (e.g. OSHA PELs, NIOSH RELs).

Whenever testing of the atmosphere indicates levels of oxygen, flammability, or toxicity that are

not within acceptable limits, entry should be prohibited until appropriate controls are

implemented. If the source of the contaminant cannot be determined, precautions should be

adequate to deal with the worst possible condition in the confined space. If there is the

possibility that the confined space atmosphere can become unacceptable while the work is in

progress, the atmosphere should be constantly monitored and procedures and equipment should

be provided to allow the employees to quickly and safely exit the confined space.

13.10. ISOLATION AND LOCKOUT/TAGOUT SAFEGUARDS

All energy sources which are potentially hazardous to confined space entrants should be secured,

relieved, disconnected and/or restrained before personnel are permitted to enter the confined

space. Equipment systems or processes should be locked out or tagged out or both per 29 CFR

1910.147 and ANSI Z244.1-1982, Lockout/Tagout of Energy Sources prior to permitting entry

into the confined space. The current lockout/tagout program being used at the site should be

used as guidance. In confined spaces where complete isolation is not possible, provisions should

be made for as rigorous an isolation as practical. Special precautions should be taken when

entering double walled, jacketed, or internally insulated confined spaces that may discharge

hazardous material through the vessel's internal wall.

Where there is a need to test, position or activate equipment by temporarily removing the lock or

tag or both, a procedure should be developed and implemented to control hazards to the

occupants. Any removal of locks, tags, or other protective measures should be done in

accordance with ANSI Z244.1-1982.

13.11. INGRESS/EGRESS SAFEGUARDS

Means for safe entry and exit should be provided for confined spaces. Each entry and exit point

should be evaluated to determine the most effective methods and equipment to be utilized to

enable employees to safely enter and exit the confined space.

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