Air in the space will become asphyxiating because there is not enough oxygen.

The space is large enough to enter, has limited or restricted entries or exits and is not designed for continuous occupancy.

Entrants should wait trained competent rescuers to arrive, because self-rescues may aggravate the hazardous conditions.

The confined space contains hazards in the air, could trap you inside the space, contains slip and fall hazards and contains hazards that you might be unable to see.

Hazards in the air of the confined space are asphyxiating, toxic, flammable or explosive.

An atmosphere that contains atmospheric concentration of any substance for which a dose or a permissible exposure limit is published in Subpart G, Occupational Health and Environmental Control, or in Subpart Z, Toxic and Hazardous Substances, of this 29 CFR 1910 and which could result in employee exposure in excess of its dose or permissible exposure limit is considered hazardous.

A confined space has only one entrance or exit.

Mechanical equipment could accidentally restart in within the confined space.

An atmosphere that contains airborne combustible dust at a concentration that meets or exceeds its lower flammable limit (LFL) is considered hazardous. NOTE: This concentration may be approximated as a condition in which the dust obscures vision at a distance of 5 feet (1.52 m) or less.

Excessive noise above the permissible exposure limit occurs in the confined space.

A confined space permit does not require names or signatures when it is properly posted.

Occurrence of an emergency, followed by properly executed recue procedures is (usually) is proof of an effective program.

The confined space contains flammable or explosive atmospheres contain gases, vapors or dusts in concentrations great enough to ignite or combust.

Examples of engulfment hazards include, soil around an excavation, grain in a silo, and powdered material in a bin.

It is never OK for an untrained worker to enter a confined space?

An atmosphere that contains an atmospheric concentration of any substance that is not capable of causing death, incapacitation, impairment of ability to self-rescue, injury, or acute illness due to its health effects is considered hazardous.

You see that two workers have collapsed. You call for help, then go in.

Of the people that die each year from confined space incidents, many of those are people trying to rescue injured entrants?

Attendant, who is stationed outside one or more permit spaces and monitors the authorized entrants, can enter a PRCS to perform a rescue without being relieved by another attendant.

Grain silos are not confined spaces.

A toll booth meets the definition of a confined space.

A space that is confined and does not contain or have the potential to contain any hazard capable of causing death or serious physical harm.

An atmosphere that contains flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL) is considered hazardous.

The confined space contains atmospheric oxygen concentration below 19.5 percent or above 23.5 percent.