Summary

  • Modern cargo holds use composite linings and advanced fire suppression systems to minimize fire risks and improve passenger safety.
  • Airbus highlights three key features for fire-proof cargo holds: air-tight and fire-proof compartments, cargo fire detection systems, and cargo fire suppression systems.
  • Fire detection systems alert pilots within one minute, allowing them to discharge Halon gas for effective suppression, ensuring safe landings even in case of cargo hold fires.

There was a time when cargo holds on commercial aircraft were made accessible during flight, so crew members could manually extinguish fires in a usual event. Newer, larger, class D cargo compartments limited the in-flight accessibility, driving the need for more stable and automated fire systems. Larger cargo holds also posed a significant risk of onboard fires, particularly due to large volumes of oxygen. Cargo holds on modern airliners are built with specialized composite linings to minimize fire risk. Moreover, more effective fire suppression systems are installed to detect, warn, and suppress in-service fires.

Historical events that led to modern cargo hold designs several in-service fire incidents have occurred in cargo compartments, driving the evolution of cargo hold designs. In August 1980, Saudia Flight 163 faced a cargo compartment fire incident, leading to the deaths of all 287 passengers and 14 crew members, mostly from smoke inhalation. In May 1996, ValuJet Flight 592 crashed in the Everglades near Miami after a cargo compartment fire, killing all 100 people onboard. Findings from both incidents showed incompetency of the fire system, including delayed alerts to pilots.

Valu592-2

Following the tragic events and lessons learned from the investigation findings, the Federal Aviation Administration (FAA) mandated that lower-deck cargo compartments be fireproofed. In the years following that, both the existing aircraft and newer models received standardized fireproofing and more efficient alerting systems for pilots to act fast in case of a cargo hold fire.

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Cargo Hold Fire: The Story Of ValuJet Airlines Flight 592

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New cargo compartment design

Commercial aircraft’s cargo compartment fire protection level was significantly improved, making passenger and cargo flights much safer. The modern commercial fleet is equipped with three key features, as described by Airbus,

  1. Air-tight & fire-proof cargo holds
  2. Cargo fire detection systems
  3. Cargo fire suppression systems

Airbus states these three features are the most important when designing a fire-proof cargo hold system. While there can always be some fire risk, the three redundant systems significantly minimize fire risks.

Inside the cargo area of an Airbus A321 P2F Freighter.

Photo: Airbus

According to Airbus,

“Lower deck cargo holds are constructed out of their doors, and many composite panels attached to the aircraft’s primary and secondary structure. Various categories of panels are used, including ceiling, sidewall, sloped and floor panels.”

“Together with their fasteners, secondary structure, and the cargo door, these panels create the liner of the cargo hold lining. This liner is required to provide the two fire protection functions of air-tightness and fire-proofing.”

Limiting oxygen in the cargo hold

The airtightness of the cargo hood limits the amount of oxygen present in the cargo hold, preventing fires in flight. This is one of the key safety features to ensure that fire is suffocated by the lack of oxygen, even if it is somehow ignited. The state-of-the-art fire suppression systems use Halon gas within the enclosed space.

Caitlin Auktweenna "auk" Tozier in an Alaska Air Cargo 737-700BCF Hold

Photo: Joe Nicholson | Alaska Airlines

Airtight seals are inserted between the panels and the structure to prevent oxygen-rich air from seeping in. The self-adhesive seals are made of elastomer foam tapes applied to the rear of the cargo hold panels. The tightening of fasteners compresses the tape, forming a tight seal in the system.

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Fireproofing the cargo compartment

Cargo hold liners and panels withstand burning in an unusual fire event. High thermal-resistant materials protect passenger cabins from fire, smoke, and other hazardous gases. The linings maintain airtightness even during larger fire events.

Airworthiness regulations define the flame-resistance properties of the cargo compartment and the materials used within. Modern aircraft equipment and systems must comply with the regulations, including testing crucial equipment.

Detection and suppression of fire

  • Sufficient Halon must be released to achieve a volumetric concentration of 5% of the compartment air.
  • Following this, a concentration of 3% must be continuously maintained for the rest of the flight.
  • With this approach, lower-deck cargo compartment fires can be suppressed for up to 360 minutes on wide-body aircraft.
McDonnell Douglas MD-11 F N290UP ex Swissair, ex Varig, now United Parcel Service cargo hold

Most commercial incidents involving cargo compartment fires showed that fire detection and alerting systems were delayed in relaying fire alerts to pilots in the cockpit. The pilots’ ability to act fast in counteracting the fire and bringing the aircraft safely to the ground depends on how soon they are aware of the fire.

Fire detection systems are designed to alert pilots within one minute of a fire starting. The new suppression systems are designed to detect and alert pilots within one minute of the start of the fire. As such, pilots can discharge Halon gas, an effective suppression agent, into the appropriate cargo hold.

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Cargo Hold Space Could Be Used For Passengers

According to Airbus,

“To achieve the extinguishing effect, sufficient Halon needs to be released to achieve a volumetric concentration of 5% of the compartment air as a first shot, for a fire knock-down effect. Following this, a concentration of 3% must be continuously maintained for the rest of flight. With this approach, lower deck cargo compartment fires can be suppressed for up to 360 minutes on wide-body aircraft.”

Multiple redundancies within the fire suppression system ensure that cargo compartment fire events are addressed effectively and safely.

What are your thoughts on the modern fire detection, alerting, and suppression systems onboard commercial aircraft? Share your views in the comments section.

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