How aviation crew face slow poisoning in the air

Aero toxicity is an area of concern especially with the advent of pressurised cabins

How aviation crew face slow poisoning in the air
Representative image. Source: Unsplash

On February 2, 2012, an aircraft took off from Sweden's Bromma Stockholm Airport for a scheduled flight to the Malmö/Sturup Airport. After approximately five minutes, the commander was affected by dizziness and nausea and, therefore, handed over the controls to the co-pilot. The flight was discontinued and the aircraft diverted back towards Bromma. 

Captain Andrew Myers, worked for JetBlue for 15 years but then in 2017, he became ill with several alarming health conditions, including toxic encephalopathy, which is a neurologic and neurocognitive disorder also involving visual difficulties, which could be permanent. The State of Oregon Workers’ Compensation Board, in August 2020, ruled in favour of Myers, which in essence establishes the fact that Myers did indeed fall ill from toxic cabin air. This decision is significant because, for years, the airline industry has denied the existence of what is known as aerotoxic syndrome, or exposure to toxic cabin air.

Myers will now be paid several years of compensation for loss of earnings and have his medical bills paid. "It’s the first case in the US to establish that the fumes that injured Myers are dangerous, though Myers is far from alone in his injuries," Glen Lasken, Myers’ attorney, told The Independent.

While the regulators and aircraft manufacturers continue to defend their stand that air quality was being maintained within safety standards, there have been numerous crew members and passengers reporting about sickness onboard or after the completion of the flight. That Boeing is well-aware of the toxicity of bleed air is indisputable. It was sued in court in the US by a flight attendant named Terry Williams though the matter was settled out of court in 2010.

Cabin air quality

The day before the Sweden incident, flight attendants and customers on the plane Captain Myers was scheduled to fly reported a strong, foul odour in the cabin while descending for landing. A fume event was written up for maintenance to resolve.

The next day before takeoff, Captain Myers and his First Officer (FO) Dirk Murray attempted to isolate the source of the fumes by performing three engine runs. During the first run, Captain Myers smelled the foul odour throughout the plane, but the FO, who remained in the cockpit, did not. During the second engine run, both smelled a very apparent choking and burning odour similar to that of dirty socks or an oily smell.

Both immediately developed headaches, began coughing and had to leave the plane to get fresh air. Captain Myers fell on the jetway and a mechanic ran up the stairs to the plane saying, "Oh my God. There’s a haze in here."

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Captain Myers and the FO re-entered the plane for the third engine run with the odour still strong. Captain Myers was coughing, his eyes stinging and watery, and the right side of his body was shaking. He had mild shortness of breath, headache and congestion. He also experienced numbness in his forearm and hand that resolved only after a couple of days.

Aerotoxic syndrome 

Aerotoxic syndrome is organophosphate poisoning resulting from exposure to bleed air. The most common but debilitating symptoms include chronic fatigue, severe headache, cognitive dysfunction, paraesthesia, ataxia and mood swings (Winder, C and Balouet, JC -- Aerotoxic syndrome). These are all, individually or collectively, enough to ground a pilot on the spot and render cabin crew unfit for further duty.

Long-term–low-level (LTLL) contamination, such as that to which aircrew are exposed, is more injurious than short-term acute exposure. Aircrew members breathe the low-level toxic air every minute of their working days. When an aircraft lands, the passengers disembark, but the crew turn around and do it all over again, time and time again. Perhaps there has been too much emphasis on fume events, while the real damage is being done by LTLL.

Remedial treatment starts with removal from the toxic environment. For aircrew, this involves cessation of employment. The longer this is delayed the more intense the affliction and the more difficult the recovery. In a lot of cases, where brain damage has been allowed to go too far, full recovery has been impossible. A striking observation is a connection between exposure and symptom onset (Winder, C and Balouet, J-C -- Aerotoxic syndrome).

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The reverse is also striking: recovery, sometimes only partial, is possible only in the absence of further exposure. This should not have come as a surprise to the industry. The bleed air system for passenger airliners was taken from the military aviation industry. In the 1950s, the United States Air Force pilots were complaining of a mysterious illness, which was traced to their exposure to the oil contamination of bleed air that heated and pressurised their fighters, bombers and transport aircraft.

HEPA filters are inadequate protection

The recirculated air is often filtered using a High-Efficiency Particulate Air (HEPA) filter which removes microorganisms and other particulate contaminants but does not remove other contaminants such as volatile organic compounds (VOCs) (Judith Anderson and Dr Nlichaelis testimony; Exs 13 9-155 and 141-4). Apart from noticeable fume events, pilots are chronically exposed to engine vapours that continuously leak through the oil seals in tiny amounts because the use of pressurised air to seal the jet engine’s bearing chamber and provide ventilation for the cabin guarantees that fugitive low-level oil emissions will enter the breathing air supply during normal engine operations (Judith Anderson and Dr Nlichaelis testimony; Ex. 142, pages 3 and 5).

US Congress concerned

"On September 19, 2019, the United States Congress expressed its "deep concern" to JetBlue Airways regarding:

1. The significant number of severe fume events over the past few months, which posed a significant health risk to in-flight crew members and passengers.

2. A disturbing pattern of fume events onboard JetBlue aircraft.

3. JetBlue’s attempt to skirt Federal Aviation Administration's (FAA) reporting standards and workers’ compensation by reclassifying ‘fume events’ or ‘cabin air safety events' as ‘odour events’. That last concern raised significant doubt with Congress regarding JetBlue’s intention to faithfully adhere to the existing health, safety, and labour laws. In light of the prevalence of flight crew members developing neurological problems following toxic gas exposures on planes, JetBlue added ‘fume events’ to its required documentation.

The cabin air quality may have a long-term detrimental effect on the health of airline crew members. The substance tricresyl phosphate (TCP) is used in jet engine oils. A neurotoxic isomer of TCP, triorthocresyl phosphate (ToCP) can, under some conditions, form an aerosol in the event of oil leakage from the engine. This aerosol can contaminate the air onboard the aircraft via the air conditioning system. However, the required amount of ToCP to reach the threshold value is so high that the risks may be considered negligible. 

Representative image

In the UK, the Department for Transport Aviation Health Working Group (AHWG) commissioned Cranfield University to carry out air cabin monitoring for contaminants on 100 flights across five different aircraft types – the BAe 146, the Boeing 757 and the Airbus A319, A320 and A321. A series of air samples were taken at defined points during all phases of flight (climb, cruise and descent) to detect and identify any VOCs, semi-VOCs, particles and carbon monoxide. In the case of some of the substances tested for, the European Standard, ‘Aircraft Internal Air Quality Standards, Criteria and Determination Methods’ (BS EN 4618: 2009) had set health and safety limits. In the absence of a specific cabin standard or limit, the study referred to other standards and guidelines established for domestic or occupational exposures.

The report, published in March 2011, found that no guidelines or standards were exceeded. Specifically, the Workplace Exposure Limits (WELs) established by the Health and Safety Executive (HSE) for organophosphates – including triorthocresyl phosphate (ToCP), the most toxic form of TCP, and tributyl phosphate (TBP) – were not breached. Indeed, it was noted that in 95% of the cabin air samples, no detectable amounts of ToCP or other TCPs were found. TBP was detected more routinely, but not in the majority of samples; TBP levels were highest during the engine start. Levels of other substances, such as carbon monoxide, toluene and xylenes, were comparable to levels of indoor pollutants seen in domestic settings.

EASA study on cabin air quality

Crew display high level of antibodies

In a recent exploratory study, auto-antibodies in serum against several proteins present in the (central) nervous system were measured (Abou-Donia et al, 2013). These auto-antibodies may be formed and released into the bloodstream upon damage to the cells of the nervous system. Serum samples of 34 flight crew members with the central nervous system (CNS)-related complaints and of 12 healthy age-matched people that had no connection with the aviation industry and no neurological symptoms were analysed. Although the auto-antibody levels of the two groups showed some overlap, the levels of auto-antibodies were clearly (much) higher in many aircrew members. In addition, one case subject showed an increase in auto-antibodies shortly after flying, which decreased only slowly over subsequent months of non-flying. 

mindFly analysis

Aero toxicity is an area of concern especially with the advent of pressurised cabins. There is a need for an international body like the International Civil Aviation Organisation (ICAO) to come up with regulations specifying the standards of cabin air quality and mitigation strategies. While the ICAO has agreed and issued the Cir 344-AN/202, Guidelines on Education, Training and Reporting Practices related to Fume Events, it remains a guideline for reporting till intense research work is carried out and published for public benefit. Aircraft manufacturers and airlines have compensated individuals possibly for the detrimental effects to their individual health due the quality of cabin air but the majority are still at large, exposed to the same toxins.

(This article first appeared in safetymatters.com)