A body belt is designed to be worn around the waist and to provide an attachment point for a lanyard or a deceleration device. This matches the description exactly: a strap that secures at the waist and has a way to connect the fall-arrest equipment. A safety harness, by contrast, is a full-body system with shoulder and leg straps that distribute fall-arrest forces across the body, not just at the waist. A waist strap alone is just a belt and may not provide the proper attachment points for a lanyard or deceleration device. A lanyard clip is just a hardware connector, not the belt itself.

Induced-draft blowers are used to remove the gases produced when fuel is burned in the furnace or boiler. The combustion process creates hot, buoyant exhaust that must be vented outdoors to prevent buildup and to keep the system safe and efficient. By pulling these combustion byproducts through the vent stack, the blower carries out the products of combustion—primarily carbon dioxide and water vapor, along with any trace gases—out of the building. The other options aren’t what the blower is designed to exhaust: condensation is moisture that can form in some systems, ventilation refers to general air exchange, and evaporation is a phase change, not the specific exhaust function of the device.

Smoke detectors in HVAC systems are installed to quickly shut down the air handling unit when smoke is detected, preventing smoke from being spread through the building. When a single rooftop unit serves multiple floors, each floor ideally represents a separate zone that needs monitoring. This ensures that if smoke is detected on one floor, the system can respond appropriately for that zone without unnecessarily shutting down airflow to all floors. In this setup, there are three floors served by the unit, so one detector per floor is required, totaling three detectors. The unit’s size or airflow (20,000 CFM) doesn’t determine the number of detectors; it’s the number of separate zones or floors that matters.

The cad cell is a flame detector. It works as a photoelectric sensor that responds to the light emitted by the flame. When a flame is present, the light lowers the cadmium sulfide cell’s resistance and sends a signal to the burner control to keep the fuel flowing. If the flame goes out, the signal changes and the control shuts off the fuel to prevent unburned oil. It’s not measuring pressure or noise, and it’s not reacting to general ambient light—it’s specifically detecting the flame’s light.