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Organophosphate and Amine Contamination of Cockpit Air in the Hawk, F-111 and Hercules C-130 Aircraft

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Abstract

A survey of cockpit air contamination by organophosphates and amines in the Hawk, F-111 and Hercules C-130 aircraft was undertaken. The air contamination occurred via the engine bleed air supply. The source of tricresyl phosphates, phenyl-α-naphthylamine and dioctyldiphenylamine was jet engine oil while hydraulic fluids are suspected of contributing to the presence of trialkyl phosphates. The concentrations of all contaminants measured were generally very low. Tricresyl phosphate concentrations were below 4 μg/m3 with two exceptions (21.7, 49 μg/m3, Hawk) compared to the maximum permissible concentrations (100 μg/m3 ). Ground engine starts, at high power, gave rise to the highest concentrations. Phenyl-α-naphthylamine and dioctyldiphenylamine concentrations were also very low (<0.06 μg/m3) in the Hercules C-130 and the absence of exposure limits for the two compounds reflects on their apparent low toxicity. Trialkyl phosphates were also found in the F-111 and Hercules C-130 aircraft at concentrations (<6 μg/m3) similar to tricresyl phosphates. They are of lower toxicity than the latter compounds and are not expected to present a health risk.

Executive Summary

Cockpit/cabin air supply, in most jet aircraft, is drawn from the compressor stage of the engine through the Environmental Control System (ECS) where the air is cooled by passage through the air/air and air/water heat-exchangers. The air is then passed through a synthetic wax impregnated (coalescer) bag which removes condensed water. The engine bleed air is prone to contamination from engine oil in the event of leaky oil seals and/or intake of contaminants such as oil and hydraulic fluids by the engine. During the 1990s air contamination incidents aboard the BAe 146 passenger aircraft were widely publicised in the media. Some passengers and crew exposed to those incidents have subsequently claimed to be suffering from chronic health problems. In 1999, an Australian Senate inquiry into aircraft safety investigated these incidents and claims. Submissions were made by some academics that the health effects were due to contamination of the bleed air by tricresyl phosphate (TCP) additive present in the jet engine oil as an anti-wear agent. Although air samples were taken by Ansett airlines, the presence of TCP could not be quantified. However, the air sampling procedure, as described in the Senate inquiry, was flawed. It was also claimed that contamination by the anti-oxidant amine additive, phenyl-α-naphthylamine, may also occur and it has been suggested that the compound causes sensitisation and may be carcinogenic. Despite the speculation, the cabin air concentrations of these potential air contaminants have never been reported. The engine bleed air (ECS) is also common to Australian Defence Force aircraft and therefore there may be adverse health effects arising from contamination of the engine bleed air supply. There is a history of incidents of smoke in the cockpits of the Hawk and F-111 aircraft and there have been reports of “smelly� bleed air in the Hercules C-130 aircraft. As a result, the Directorate of Air Force Safety initiated a RAAF sponsored DSTO task to investigate bleed air contamination in ADF aircraft. Three aircraft types have been surveyed, Hawk, F-111 and Hercules C-130. Air sampling of the cockpit air in the Hawk was performed on the ground when the Auxiliary Power Unit was operated, since the main engine does not appear to cause smoke in the cockpit. The highest concentrations of TCP measured were 21.7 and 49 μg/m3, but the remainder of the 15 Hawk air samples showed <1.5 μg/m3 of TCP. In the case of the F-111 and Hercules C-130 aircraft, cockpit air was sampled during ground engine power runs and in flight. The concentrations of TCP measured during ground power runs for the F-111 and Hercules C-130 were <3.5 μg/m3 and <0.3 μg/m3 respectively. Those obtained during flights were <1 μg/m3 and <0.2 μg/m3 respectively. These concentrations are very low compared with the maximum permissible timeweighted 8 hour average (TWA) exposure of 100 μg/m3 for TCP which is based on the tri-o-cresyl phosphate component. In most cases the most toxic components of TCP (mono-o-cresyl phosphate isomers) calculated to be present in the cockpit air corresponded to less than ca. 1/200 of the TCP TWA allowing for the fact that these are 10 times more toxic than tri-o-cresyl phosphate. Two air samples taken from the cockpit of the Hawk indicated relatively high concentrations of TCP. One sample (49 μg/m3) was associated with an oil spill in the vicinity of the engine (APU) air intake. As the air sample was taken with the cockpit canopy opened, excessive TCP concentrations (> 100 μg/m3) may have occurred if the canopy had been closed. As a general rule it is recommended that the ADF consider total TCP air concentrations <1 μg/m3 as a desirable target rather than the statutory exposure limits of 100 μg/m3. This recommendation is based on the uncertainty of toxicity data, the absence of economic imperatives (which provide a rationale for establishing a high exposure level in industry) and the potential for cognitive effects on the flight crews. The target levels appear to be readily achievable and are indicative of the satisfactory condition of the compressor oil seals. In addition to TCPs, trialkyl phosphates were found to be present in the cockpit air of the F-111 and Hercules C-130 aircraft. These are probably due to hydraulic fluid contamination of the engine bleed air and they are present at concentrations slightly higher than TCP. However, because of their low toxicity they are unlikely to pose a health risk. Similarly, the concentrations of phenyl-α-naphthylamine and dioctyldiphenylamine in the flight deck air of the Hercules C-130 aircraft were found to be very low (< 0.1 μg/m3) and are likely to be inconsequential due to the low toxicity of these compounds. Although the concentrations of these bleed air contaminants were very low and unlikely to produce any adverse health effects, washing the ECS heat exchangers with a solvent such as acetone, when maintenance permits, could further reduce the levels. Furthermore, the coalescer bags serve to trap some of the TCP (and most likely the amines and trialkyl phosphates) and frequent replacement of these would also reduce the cockpit air contamination. However, these measures will not affect smoke incidents in the F-111 (and Hawk aircraft). This may best be achieved by the installation of a HEPA (high efficiency particulate air) filter in the ECS ducting. It is also recommended that further research be carried out to identify and quantify the air contaminants arising from the thermal decomposition of the oil base which characterise the smoke and odour during episodes of engine bleed air contamination.

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