Combustion Safety Principles Flashcards

What is the primary purpose of a combustion air opening in a mechanical room?

Answer: To provide adequate oxygen for complete combustion

Combustion air openings supply sufficient oxygen to support complete combustion and prevent CO production from fuel-fired appliances.

During a worst-case depressurization test, which combination of conditions is typically induced?

Answer: All exhaust fans on, fireplace damper open, supply fans off

Worst-case depressurization maximizes negative pressure by operating all exhaust devices and opening fireplace dampers simultaneously.

A gas water heater located in a garage must have its burner and pilot elevated at least how high above the floor?

Answer: 18 inches

Garage-installed water heaters must have ignition sources elevated at least 18 inches above the floor to avoid igniting gasoline vapors that pool at floor level.

Which test instrument is used to measure carbon monoxide concentration in appliance flue gases?

Answer: Combustion analyzer

A combustion analyzer measures CO, CO2, O2, and flue gas temperature to assess combustion efficiency and safety.

What does a yellow or orange burner flame on a natural gas appliance most likely indicate?

Answer: Insufficient combustion air causing incomplete combustion

Yellow or orange flames indicate incomplete combustion from insufficient air, which can produce dangerous levels of carbon monoxide.

What is the term for the phenomenon where combustion appliance exhaust is pulled back into the living space through the flue?

Answer: Backdrafting

Backdrafting occurs when negative house pressure or adverse weather conditions reverse the intended upward flow of combustion gases through the flue.

Which RESNET standard governs combustion safety testing procedures for HERS raters?

Answer: RESNET/ICC 380

RESNET/ICC 380 establishes standard test methods for building enclosures, including combustion safety diagnostics performed by HERS raters.

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

Answer: 1,200 ppm

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

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

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

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

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

Answer: Slightly negative or neutral relative to outside

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

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

Answer: Backdrafting because the oversized flue reduces draft velocity

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

What does CO ppm stand for in combustion testing?

Answer: Carbon monoxide parts per million

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

Which type of venting system is most resistant to backdrafting caused by house depressurization?

Answer: Category IV sealed direct-vent system

Direct-vent (Category IV) systems draw combustion air from outside and exhaust directly outside through sealed concentric pipes, making them immune to indoor pressure fluctuations.

If a combustion analyzer reads 400 ppm CO in the undiluted flue gas of a gas furnace, what action should a HERS rater take?

Answer: Advise the homeowner of a potential safety hazard and recommend HVAC service immediately

400 ppm CO in undiluted flue gas exceeds safe thresholds and indicates incomplete combustion requiring immediate professional HVAC inspection and repair.

The spillage test for a naturally vented water heater is typically performed by holding a smoke pencil or mirror near the draft hood opening. A passing result shows:

Answer: Smoke drawn into the draft hood and up the flue

Smoke drawn into the draft hood indicates proper upward draft pulling combustion gases safely out of the home.

What is the typical worst-case depressurization threshold (in Pascals) at which natural-draft combustion appliances are considered at high risk for sustained backdrafting?

Answer: -5 Pa

A CAZ pressure at or below -5 Pa relative to outside under worst-case conditions indicates high backdrafting risk for naturally vented appliances.

Which fuel produces carbon monoxide when burned with insufficient oxygen?

Answer: Any carbon-containing fuel

Any fuel containing carbon—natural gas, propane, oil, wood, coal—can produce CO when combustion is incomplete due to insufficient oxygen.

A combustion safety inspection reveals an improper connector material: single-wall black iron pipe passing through a bedroom wall to the chimney. The correct action is:

Answer: Flag it as a hazard—single-wall connectors must not pass through living spaces

Single-wall flue connectors are not permitted to pass through or be concealed in walls, floors, or ceilings due to CO leak and fire risk.

During a combustion safety test, which appliance configuration typically creates the greatest depressurization of the combustion appliance zone?

Answer: A large central-return air handler drawing air from the CAZ

An air handler with a return located in the CAZ can draw large volumes of air from that zone, dramatically depressurizing it and inducing backdrafting in co-located appliances.

What is the purpose of a draft diverter (draft hood) on an atmospheric water heater?

Answer: To dilute flue gases with room air and protect the burner from downdrafts

The draft hood mixes room air with flue gases to moderate temperature and prevents downdrafts from extinguishing the pilot or burner.