This video from Total Safety provides a great example of proper test procedures for permit-required confined spaces required by OSHA 1910.146.

http://www.youtube.com/watch?v=3J_AFyis9M8&feature=player_embedded#at=15

Non-Permit Confined Space vs. Permit Required Confined Space

There are very specific definitions that help identify whether or not a confined space requires an entry permit and a pre-entry checklist. 

Non-Permit Confined Space

A Non-Permit confined space does not contain or have the potential to contain any hazard capable of causing death or serious physical harm.
Examples of non-permit required confined spaces include:

• Interiors of HVAC units
• Certain air plenums and pipe chases
• Attics
• Walk-in freezers or refrigerators
• Some building crawl spaces

Permit Required Confined Space

OSHA uses the term "permit-required confined space" ( or 'permit space') to describe a confined space that:

• Contains or has a potential to contain a hazardous atmosphere.
   
• Contains a material that has the potential for engulfing an entrant.
   
• Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section.
   
• Contains any other recognized serious safety or health hazard, such as unguarded machinery, exposed live wires, or heat stress.