No worker is allowed to enter a confined space if airborne combustible dust or mist is present in a concentration sufficient for explosion. If an explosive or flammable atmosphere is detected, you can perform only certain types of work.
The conditions for each type of work are specified below the following
definitions.
Hot work means activities that could produce a source of ignition such as a spark or open flame. Example of hot work include welding, cutting, grinding, and using non-explosion-proof electrical equipment.
Cold work means activities that cannot produce a source of ignition.
a) Between 0% and 5% of the LEL, you can perform hot work. The
following conditions must also be met:
 The oxygen content must be maintained below 23%
 The atmosphere must be continuously monitored.
 The entry permit must include adequate provisions for hot work, and
it must specify the appropriate measures to be taken.
 An alarm and exit procedure must be in place to provide
adequate warning and allow safe escape if the atmospheric
concentration exceeds 5% of the LEL or if the oxygen content
exceeds 23%.
b) Between 0% and 10% of the LEL, you can perform cold work.
c) Between 0% and 25% of the LEL, you can perform inspection work only.
Alternatively, work may be carried out in the confined space if the
combustible, explosive or flammable atmosphere is rendered inert by an inert gas (such as nitrogen, argon, helium, or carbon dioxide).
Inerting is the process of replacing the potentially combustible atmosphere in a confined space with a noncombustible gas such as nitrogen, argon, helium, or carbon dioxide.
The atmosphere must be monitored continuously to ensure it remains inert.
The worker in the confined space must use adequate respiratory equipment as well as adequate equipment to help people outside the confined space locate and rescue the worker if a problem occurs.

The inert gas will replace all of the oxygen as well as the combustible gases in the confined space.
Workers entering the confined space must use NIOSH-approved air-supplied respirators. After work is completed, the confined space must be properly ventilated, and a competent worker must test the confined space to see if it is safe.