Fire Protection - Cargo Compartment 
- QRH - CARGO FIRE
- Limitations - Fire Protection
Cargo Compartment Fire Protection
Cargo Compartment Fire Protection consists of these systems:
- Cargo Compartment smoke detection.
- Cargo Compartment Fire Warning.
- Cargo Compartment Fire Extinguishing.
Cargo Compartment Smoke Detection
The forward and aft cargo compartments each have dual smoke detectors installed.
Each cargo compartment has two fans that can draw air through the smoke detectors. Only one fan operates at a time. The second or standby fan starts automatically on sensing a failure of the operating fan.
During normal operations, both detectors in each compartment must sense smoke to activate fire warnings. When smoke is detected the associated Cargo Fire Warning Light illuminates and the EICAS warning FWD/AFT CARGO FIRE displays.
The SYSTEM FAIL light illuminates and the EICAS advisory message FIRE/OVHT SYS displays to indicate failure of the Cargo Compartment smoke detection system. An EICAS status message indicates the inoperative loop. The SYSTEM FAIL light and advisory message can be reset to allow monitoring of the remaining systems.
Fault monitoring of the cargo smoke detectors only occurs when the Fire Protection system is tested. When a fault is detected, the systems reconfigures itself for single detector operation. The operating smoke detector is still capable of activating the cargo warnings.
Cargo Compartment Fire Warning
The indications of a cargo compartment fire are:
- The fire bell sounds.
- The master WARNING lights illuminate.
- The FWD or AFT cargo fire warning light illuminates.
- The discrete FIRE warning light illuminates.
- The EICAS warning message FWD or AFT CARGO FIRE displays.
The fire warning lights remain illuminated as long as the fire signal exists. The fire bell may be silenced by any of the following actions:
- Extinguishing the fire and clearing the smoke.
- Pushing either Master WARNING/CAUTION Reset Switch.
- Pushing the illuminated cargo compartment ARMED switch.
The fire warning bell rings intermittently for 2 seconds on, then 3 seconds off.
Cargo Compartment Fire Extinguishing (757-200)
Two fire Extinguisher bottles are installed for cargo compartment fire extinguishing. Pushing the FWD or AFT cargo compartment ARMED switch:
- arms the extinguishers for that compartment
- Silences fire warning bell
- Turns off the respective cargo heat system
- Opens overboard exhaust valve
In addition, arming the forward system:
- Turns off both the left and right air conditioning recirculation fans
- Switches both air conditioning packs to high flow mode
In addition, arming the aft system:
- Turns off the right air conditioning recirculation fan
- Switches the right air conditioning pack to high flow mode
Pushing the number 1 cargo fire bottle discharge switch, discharges the number 1 fire bottle into the armed compartment. The number 1 cargo fire bottle DISCH light illuminates and the EICAS advisory message CARGO BTL 1 displays to indicate low extinguisher bottle pressure.
The number 2 fire extinguisher is manually discharged later in flight (after 80 minutes or during approach, whichever occurs first) to maintain the required concentration of extinguishing agent in the affected compartment. The DISCH light and the EICAS advisory message CARGO BTL 2 displays to indicate low extinguisher bottle pressure.
Cargo Compartment Fire Extinguishing (757-300)
Fire Extinguisher bottles are installed for cargo compartment fire extinguishing. Pushing the FWD or AFT cargo compartment ARMED switch:
- arms the extinguishers for that compartment
- Turns off both left and right air conditioning recirculation fans
- Opens overboard exhaust valve
- Switches both air conditioning packs to high flow mode
- Silences fire warning bell
- Turns off the respective cargo heat system
The fire extinguishing system fitted to the 757-300 is modified to allow for the 33% greater cargo volume.
Pushing the cargo fire bottle discharge switch initiates discharge of both fire bottles. The first bottle discharges immediately into the selected compartment. The second bottle automatically discharges either 30 minutes later or when the aircraft has landed at a reduced flow rate into the selected compartment. Total protection provided is 180 minutes.
The CARGO BTL 1 advisory message usually displays on EICAS within a few seconds of pressing the cargo fire bottle DISCH switch. The CARGO BTL 2 EICAS advisory message will display when the second bottle discharges. The DISCH light illuminates when either bottle discharges.
