Shuttle Reference Manual Space Shuttle Orbiter Systems Smoke Detection and Fire Suppression

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Smoke detection and fire suppression capabilities are provided in the crew cabin avionics bays, the crew cabin and the Spacelab pressurized module. Ionization detection elements, which sense levels of smoke concentrations or rate of concentration change, trigger alarms and provide information on smoke concentration levels to the performance-monitoring CRT system and displays on flight deck display panel L1.

The ionization detection system is divided into two groups: group A and group B. Group A ionization detection elements are located in the environmental control and life support system cabin fan plenum outlet beneath the crew cabin middeck floor and in the left return air duct on the crew cabin flight deck; and one element is located in each of the three avionics bays (bays 1, 2 and 3A). Group B ionization detection elements are located in the right return air duct on the crew cabin flight deck and in avionics bays 1, 2 and 3A. On Spacelab missions, ionization detection elements are located in the pressurized Spacelab module.

If an ionization detection element senses a smoke concentration of 2,200, plus or minus 200, micrograms per cubic meter or a rate of smoke increase of 22 micrograms per cubic meter per second for eight consecutive counts in 20 seconds, a trip signal illuminates the applicable red smoke detection A or B light on panel L1, activates the C/W master alarm red lights and sounds the siren in the crew cabin. The normal reading on the CRT for the smoke detection elements is 0.3 to 0.4. A reading on the CRT of 2.2, plus or minus 0.2, corresponds to 2,200, plus or minus 200, micrograms per cubic meter.

Fire suppression in the crew cabin avionics bays is provided by one Freon-1301 (bromotrifluoromethane) extinguisher bottle in each of the three avionics bays. Each bottle contains 3.74 to 3.8 pounds of Freon-1301 in a pressure vessel that is 8 inches long and 4.25 inches in diameter. To activate the applicable Freon-1301 bottle in an avionics bay, the corresponding fire suppression av bay switch on panel L1 is positioned to arm, and the corresponding agent disch push button light indicator on panel L1 is depressed for at least two seconds. The agent disch push button light indicator activates the corresponding pyro initiator controller, which initiates a pyrotechnic valve on the bottle to discharge the Freon-1301 into the avionics bay. When the Freon-1301 bottle is fully discharged, the push button light indicator white light will be illuminated. The white light will also be illuminated if the pressure in an avionics bottle decays before use.

The red smoke detection cabin light on panel L1 is illuminated by the smoke detection ionization element in the ECLSS cabin fan plenum, the red l flt deck fire detection light is illuminated by the crew cabin left flight deck return air duct smoke ionization element, the red r flt deck fire detection light is illuminated by the crew cabin right flight deck return air duct smoke ionization element, and the red payload fire detection light is illuminated by the smoke detection ionization elements in the Spacelab pressurized module if it is a Spacelab mission. The applicable smoke detection ionization element trips at the same levels as the avionics bay elements, illuminates the applicable red smoke detection A or B light on panel L1, activates the C/W master alarm red lights and sounds the siren in the crew cabin.

Three portable hand-held fire extinguishers are available in the crew cabin. Two are located in the crew cabin middeck and one is on the flight deck. Each fire extinguisher nozzle is tapered to fit fire hole ports in the display and control panels. The extinguishing agent is Halon-1301 (monobromotrifluoromethane). Halon-1301 minimizes the major hazards of a conflagration: smoke; heat; oxygen depletion; and formation of pyrolysis products, such as carbon monoxide. The fire extinguishers are 13 inches long. The portable fire extinguishers can also be used as a backup for extinguishers in the avionics bays.

Various parameters of the smoke detection system and remote fire extinguishing agent system are provided to telemetry.

The smoke detection circuit test switch on panel L1 tests the smoke detection system, lights and alarm circuitry. When the switch is positioned to A or B, electrical power is applied to the ACA channels controlling the agent disch lights, and the white lights are illuminated. After approximately a 20-second delay, the smoke detection A or B lights are illuminated and the siren is triggered.

The smoke detection sensor switch on panel L1 resets a tripped smoke detection element.