Twelve minutes after the take-off of flight TWA800, the plane heading from New York City to Paris exploded off the coast of Long Island and killed all 230 passengers. Originally, terrorists were blamed, but after a four-year investigation, authorities concluded that the perpetrator was a perfect storm of a fume-filled fuel tank, oxygen, and a rouge spark (Kennedy, 2021). Aviation accidents are rare, but since commercial flights began in 1959, 17 fuel tank explosions have cost 550 people their lives. A 1998 study by the Federal Aviation Administration’s (FAA) Aviation Rulemaking Advisory Committee (ARAC) even speculated that without intervention, we could expect a fuel tank explosion every four and a half years. Their calculations were not off because almost four and a half years after flight TWA800 blew up, a Thai Airways flight did the same (Evans, 2001). Addressing safety concerns is vital to keeping the aviation industry thriving, and more importantly, its passengers alive.
It has long been known that a combination of fuel, oxygen, and a spark would cause an explosion, but initial preventative measures had always focused on eliminating potential ignition sources. After 17 failures, the FAA created the ARAC to “determine what could be done to mitigate the hazard posed by flammable vapors in fuel tanks” (Evans, 2001). The space above an airplane’s fuel tank is called the ullage. With heightened temperatures, the fuel vaporizes and mixes with oxygen, creating an explosion-ready mixture. Their idea for a second fail-safe was to inert (chemically inactivate) the ullage.
Five years after TWA800, NASA released a report outlining safe fuel-tank oxygen levels are 9% oxygen and 12% oxygen respectively for military and commercial aircrafts (Reynolds et al, 2001). Nitrogen was chosen to inert the ullage because of its ready abundance from a hot and pressurized engine byproduct called “bleed air” (Agata, 2017). This “bleed air” is redirected into cylinders containing membranes, which are of thousands of hollow polymer (plastic) fibers; their wall permeability (molecular-level filter size) allows only oxygen and water vapor to escape but funnels nitrogen back to the fuel tank. Essentially, as fuel is used, the nitrogen it produces, as a byproduct, replaces the space creating a safe and self-sufficient cycle (Atlas Copco, 2021). This process, commonly referred to as fuel tank inerting, has saved hundreds of lives since its further study and eventual requirement in 2001 (Saftey, 2012).
Based on an MIT study, when flight TWA800 flew (1988-1998), the chance of a catastrophic accident was 1 in 1.3 million, but because of these and other technological advancements, that plummeted to 1 in 13.7 million between 2018 and 2022 (Dizikes, 2024). The next time you find yourself flying, even from New York City to Paris, you can relish in knowing fuel tank inerting is ensuring your plane probably won’t explode.
References
Agata Blaszczak-Boxe. (2017, September 28). Facts About Nitrogen. Live Science; Live Science. https://www.livescience.com/28726-nitrogen.html
Atlas Copco. (2021). Atlas Copco | What is membrane nitrogen generation? Atlas Copco; Atlas Copco Corporate Website. https://www.atlascopco.com/en-us/compressors/wiki/compressed-air-articles/membrane-nitrogen-technology
Dizikes, P. (2024, August 4). Study: Flying keeps getting safer. MIT News | Massachusetts Institute of Technology. https://news.mit.edu/2024/study-flying-keeps-getting-safer-0807#:~:text=The%20risk%20of%20a%20fatality%20from%20commercial%20air
Evans, D. (2001, June 1). Safety in Avionics: Time to Stop Fuel Tank Explosions. Avionics International; Avionics International. https://www.aviationtoday.com/2001/06/01/safety-in-avionics-time-to-stop-fuel-tank-explosions/#:~:text=The%20ARAC%E2%80%99s%20final%201998%20report%20predicted%20gloomily%20that
Kennedy, L. (2021, July 12). What Happened to TWA Flight 800? HISTORY. https://www.history.com/news/twa-flight-800-crash-investigation
Safety in Avionics: Time to Stop Fuel Tank Explosions. (2012, June 22). Avionics International; Avionics International. https://www.aviationtoday.com/2001/06/01/safety-in-avionics-time-to-stop-fuel-tank-explosions/#:~:text=The%20ARAC%E2%80%99s%20final%201998%20report%20predicted%20gloomily%20that
Reynolds, T., Bailey, D., Lewinski, D., & Roseburg, C. (2001). Onboard Inert Gas Generation System/ Onboard Oxygen Gas Generation System (OBIGGS/OBOGS) Study Part I: Aircraft System Requirements. https://ntrs.nasa.gov/api/citations/20010047494/downloads/20010047494.pdf