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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.
13-10


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