TRI-ORTHO-CRESYL PHOSPHATE (TOCP)
4.35 We received evidence from a number of witnesses, particularly the Organophosphate Information Network (OPIN - p 257), BALPA (p 213), and the International Association of Flight Attendants (AFA - p245), expressing concerns about the risk of TOCP poisoning for cabin occupants, particularly for crew who might be subjected to repeated exposure in some aircraft types[55], as a result of oil leaking into the cabin air supply. Although Dr Murray's examination of the London National Poisons Information Centre records and a literature search revealed no cases or enquiries about TOCP in relation to aircraft (p 96), the concerns are serious, and we pursued them further.
4.36 Tri-cresyl phosphate (TCP [56]) has, as noted by Dr Howse of Rolls-Royce, been used for many years as an anti-wear additive in aviation lubricants, at levels varying between 1-3% in currently available oils (p 271). Mr Fogarty of ExxonMobil commented that no other additive had been found to match TCP's anti-wear and load carrying performance (p 232).
4.37 TCP exists in three different forms or isomers, of which the "ortho" form (tri-ortho-cresyl phosphate - TOCP) is highly toxic. As noted by the Medical Toxicology Unit and OPIN, the most significant adverse effect of overexposure to TOCP, which might arise from improper use of the parent material such as swallowing or prolonged or repeated inhalation or skin contact, is peripheral neurotoxicity (nerve damage). This can lead to pain and serious paralysis of limbs, and bowel and lung disorders. After exposure ceases, some recovery usually ensues but a degree of permanent disability is not uncommon (pp 96 & 257).
4.38 Rolls-Royce stated that all current TCP used in the formulation of aviation lubricants contained far less than 0.1% TOCP and that, in fully formulated oils, TOCP was at practically undetectable parts-per-billion levels (p 271). ExxonMobil noted that jet engine oils formulated with TCP[57] are not classified as dangerous according to the toxicological criteria defined in the Dangerous Substances Directive (p 232).
4.39 Calculations by Airbus Industrie (Q 461 and refined in subsequent correspondence) showed that the worst-case scenario of the total discharge of an engine's lubricant into the engine would result in about 0.4 kg of oil passing into the cabin ventilation systems. Assuming that the oil contained 3% TCP, of which 0.1% was TOCP, the peak cabin atmosphere TOCP level would be about 0.025 mg/m3, reducing as a result of normal ventilation thereafter. The peak level would be a quarter of the workplace limit of 0.1 mg/m3 (and less than a tenth of the emergency workplace limit of 0.3 mg/m3). Contamination at much lower levels would result in visible smoke and odour which would normally result in the crew switching off the ventilation feed from the affected engine.
4.40 This question - including the potential effects on aircrew from any long-term exposure - has been looked at in much greater detail by a Committee of the Australian Senate inquiring into particular allegations of such contamination in the BAe 146. Although its Report[58] referred extensively to cabin air quality and chemical contamination in the aircraft, and recommended that the engine lubricating oil used (a Mobil product) be subjected to a further hazardous chemical review, it made no specific points about TCP or TOCP that have given us additional concerns[59].
4.41 The absence of confirmed cases of TOCP poisoning from cabin air and the very low levels of TOCP that would be found in even the highly unlikely worst case of contamination from oil leaking into the air supply lead us to conclude that the concerns about significant risk to the health of airline passengers and crew are not substantiated.
