HERS Combustion Safety Principles 3

Question 1

What level of ambient CO in a home (in ppm) is considered immediately dangerous to life and health (IDLH) by NIOSH?

Accepted Answer

1,200 ppm

Answer

NIOSH defines the IDLH level for CO as 1,200 ppm, at which exposure can cause death or irreversible health effects within 30 minutes.

Question 2

A Category I vented appliance relies on which mechanism to exhaust combustion gases?

Accepted Answer

Natural draft buoyancy created by temperature difference between flue gas and outside air

Answer

Category I appliances use natural draft, relying on the buoyancy of hot flue gases rising through a vertically vented system.

Question 3

When testing a atmospherically vented furnace, the CAZ (combustion appliance zone) pressure should ideally read:

Accepted Answer

Slightly negative or neutral relative to outside

Answer

A CAZ that is only slightly negative or neutral supports proper natural draft without creating conditions that cause backdrafting.

Question 4

Orphaned water heaters—left alone on a large flue after a furnace is removed—are at heightened risk of:

Accepted Answer

Backdrafting because the oversized flue reduces draft velocity

Answer

An oversized flue slows flue gas velocity and allows cold outside air to cool and reverse the flow, causing backdrafting in the remaining appliance.

Question 5

What does CO ppm stand for in combustion testing?

Accepted Answer

Carbon monoxide parts per million

Answer

CO ppm means carbon monoxide concentration expressed as parts per million, the standard unit for measuring this toxic gas in air.

(HERS) Certified Home Energy Rating System Rater Practice Test