Firefighter and EMS certification, exam by exam

5% to 15% is the range for natural gas (methane); swapping common fuels' ranges understates how little gasoline vapor it takes to burn.

2.1% to 9.5% belongs to propane, an easy mix-up because both are everyday fuels with low lower limits.

Gasoline vapor ignites between roughly 1.4% and 7.6% in air; that low lower limit means even a small spill can make an ignitable mixture.

12.5% to 74% is carbon monoxide's wide range, which is why CO-rich smoke can ignite; gasoline's range is far narrower.

Carbon monoxide is a gas that only the SCBA keeps out; a hood protects skin, not the airway.

Steam burns come from moisture and compressed gear; a particulate barrier does nothing about them.

Every structural hood already shields the ears from heat; the particulate layer was added for contamination, not thermal protection.

Particulate-blocking hoods add a filter layer so fine soot carrying carcinogens does not reach the neck and jaw, where skin absorbs it readily.

A rated stair enclosure is built to keep fire out; the balloon-frame danger is the hidden wall cavities.

Plates at each floor cut the stud channels off, which is why platform framing slows vertical spread instead of speeding it.

Balloon-frame studs run unbroken from the foundation to the roof line, so the open channels between them act as chimneys from basement to attic.

Rated gypsum ceilings resist fire passage; choosing them confuses a protective feature with a spread path.

Heat and smoke from the basement rise up the open interior stairway toward the door above, so a crew going down stands in the hottest part of the flow path.

An open stairway is a vertical opening that channels fire upward, the opposite of a fire stop.

Runoff down the stairs is a slip hazard and a nuisance, but the life threat is the heat moving up through the crew.

The intake side brings cooler air toward the fire; the stairway above a basement fire is where hot gases leave.

Slow city streets still produce crashes and rollovers, so the rule does not depend on road type.

Members are seated and belted whenever the apparatus is in motion, on every run; vehicle crashes are a leading cause of firefighter deaths, and unbelted riders are thrown from the cab.

Belts are not only for emergency runs; non-emergency trips carry the same crash risk.

The return trip is one leg among many; the rule covers every movement of the apparatus.