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The issue of aircraft air contamination due to oils and hydraulic fluids leaking into the aircraft air supply is a known problem in the aviation industry. There are a range of regulations that are in place to ensure all cases of fume contamination are reported and therefore investigated. However, there is strong evidence that the reporting system to regulatory agencies is not working and, consequently, under-reporting occurs and the fume events taking place are considerably higher than the aviation industry admits. There are a variety of reasons for this including commercial pressures, fatalism about long-standing and apparently insurmountable engineering problems, operational procedures that focus on keeping aircraft flying and a culture to minimise health and safety risks. These have significant health and safety implications for crew and passengers.

The cabin of an airplane is a specialised working environment and should be considered as such. The oils and hydraulics used in airplane engines are toxic, and specific ingredients of such materials are irritating, sensitising and neurotoxic. If oil or hydraulic fluids leak out of engines, this contamination may be in the form of unchanged oil/fluid, degraded oil/fluid from long use in the engine, combusted oil/fluid or pyrolised oil/fluid, in the form of gases, vapours, mists and particulate matter. If leak incidents occur and the oil/fluid is ingested into bleed air and is passed to the flight deck and passenger cabins of airplanes in flight, aircrew and passengers may be exposed to contaminants that can affect their health and safety. Where contamination of air in the flight deck and passenger cabin occurs that is sufficient to cause symptoms of discomfort, fatigue, irritation or toxicity, this contravenes the air quality provisions of Federal Aviation Regulations, most notably FAR 25.831. Symptoms of immediate or short-term nature and reported by exposed staff in single or few leak incidents are consistent with the development of irritation and discomfort. Symptoms of a long-term nature (that is, sustained symptoms for at least six months) reported by some exposed staff following small to moderate numbers of leak incidents are consistent with the development of an irreversible discrete occupational health condition, termed aerotoxic syndrome. Features of this syndrome are that it is associated with air crew exposure at altitude to atmospheric contaminants from engine oil or other aircraft fluids, temporarily juxtaposed by the development of a consistent symptomology including short-term skin, gastro-intestinal, respiratory and nervous system effects, and long-term central nervous and immunological effects.

Aircraft air supply contamination from leaking oil and hydraulic fluids has a long history in commercial aviation. There is a wide range of aviation legislation covering the required processes to be followed when this type of defect occurs, including reporting, maintenance procedures, airworthiness requirements, crew fitness for flight and emergency procedures. A variety of evidence showing that contaminated air has an extensive and well-documented history will be examined. It is clear that the regulations are not being adhered to or enforced. A variety of issues emanating from these failures will be reviewed as well as suggestions made as to what can be done to effectively resolve them.

Aircraft cabin air being supplied from the engines or APU is known to occasionally be contaminated with hydraulic fluids, engine oils, and pyrolysis products of these which need to be removed to ensure that the crew and passengers are not exposed to any contaminants. One way of achieving this is to filter these contaminants out of the outside air before it reaches the crew and passengers. Additionally, some aircraft cabin air is recirculated and this also needs to be filtered to remove bacteria and viruses. This chapter reviews a number of catalytic, physical, and ventilation system alternatives to simple filtration that could help to eliminate the risk of contaminated outside air or recirculated air from entering the passenger cabin.

Aircraft cabin air quality has attracted much attention, summarized recently by a detailed examination and commentary by a U.S. National Academy of Sciences Committee. Ventilation of aircraft has several significant variables that require control measures that are seldom of concern for occupied space at ground level. The principal of these special requirements are the need to compensate for the substantial difference between cabin and outside pressures, the much lower available space per occupant in aircraft cabins, and the need for coping with more extreme external temperatures than are common at ground level. The breadth of these concerns is of interest in the policies and regulatory aspects of a number of agencies which are briefly described, and their roles and areas of potential interest outlined. Types of possible contaminants are listed, and the limits which have been set by several of these agencies for many of these potential contaminants are tabulated. In addition recent measured aircraft cabin concentrations of several key contaminants are listed. This chapter provides an overview of the general air quality variables affecting enclosed space to enable these to be related to the special needs of some of the less common enclosed spaces described in the following chapters.

Concentrations of pollutants emitted in the exhaust of gasoline and diesel engines and from evaporation of fuels -- (e.g. CO, CO, NO, particulate matter, and volatile organic compounds) have been measured at elevated levels within the enclosed spaces of automobile, bus, and train cabins in urban centers throughout the world and compared to ambient air levels. The magnitude of the elevation has been linked to vehicle type, fuel composition and traffic congestion. The amount of time spent traveling and the mode of transportation used varies across the population and by location. Controls on mobile emissions have resulted in declines in the exposure to pollutants within vehicles in countries in which they have been implemented. The exposure received within cars, buses and trains is a significant portion of the total daily exposure to pollutants emitted by mobile sources.

Generally, shipboard air quality problems are not severe in comparison to those in many homes and offices. However, a number of problems have been identified which warrant attention in order to safeguard passenger comfort and health. The HVAC systems of some ships, particularly older vessels, are prone to microbial contamination. A lack of awareness of the potential problems at the design stage and subsequent lack of maintenance has allowed moulds and fungi to infiltrate the HVAC system where these collect and grow. These microbes not only pose an immediate risk of respiratory illness and allergic responses, they are also a nuisance with respect to the general maintenance and cleaning of vessels and hence are often a cause of complaint. Airborne microbial sampling has been used extensively to determine the potential for passenger exposure to this type of contamination. Due to the complexities of shipboard HVAC design, proper filtration offers the best method of keeping the system clean and preventing the accumulation of microbial contamination. Ventilation efficiency is a problem on some vessels, especially in smaller cabins or densely occupied communal areas. Thermal comfort is also a source of complaint which requires attention on many ships. Proactive monitoring to evaluate indoor air quality and identify remedial measures reduces the likelihood of problems developing. Cost-effective improvements can be made to the design and operation of ventilation systems that reduce contamination and improve air quality. It is apparent that many of the problems encountered could have been “designed out”. In particular, attention should be paid to the prevention of ingress of water into the supply and exhaust systems, thereby restricting the potential for microbial proliferation. Provision of better access for inspection and cleaning of ductwork would also be beneficial.

Atmosphere control in submarines has developed to meet the operational requirements. Until the end of WWII submarines were primarily semi-submersibles spending most of their time on the surface and submerged for periods of 12 h or less. However, rudimentary control of oxygen and carbon dioxide was available in some WWI boats. In the latter years of WWII, the requirement for longer dive times increased the demand for atmosphere control and the development of atmosphere monitoring instrumentation. The introduction of nuclear-powered submarines eliminated the need for air-dependent propulsion, and initially their dive times were limited only by air quality problems. The solution of these problems led to long-term (3 months) atmosphere control techniques, real-time air monitoring capabilities and the establishment of toxicological data for a large number of air contaminants. These developments have also impacted on atmosphere control in conventional diesel-electric submarines. More recently a new generation of submarines with non-nuclear air-independent propulsion has emerged. Although their dive times are limited to 2--3 weeks, this capability can be best exploited with the development of new energy efficient air purification technology.

Air quality in the small, closed environment of a spacecraft cabin is always a critical matter for the safety, health, and comfort of the crew. The technologies used to keep air breathable in spacecraft have a unique set of requirements because of several constraints that become more important as the duration and distance of space missions lengthen. Technologies must be extremely robust, as supplies and spare parts are few and resupply may be impossible. They must be well coordinated and function in a tightly integrated life-support system. Mass, volume, and power consumption must be minimal due to the high cost of launch mass and limited solar/battery energy. This article examines some of the issues associated with spacecraft air revitalization and briefly reviews some of the technologies developed to maintain quality and minimize waste through recycling of air. We emphasize approaches for long-duration missions (i.e., more than one month), in which technologies need to be regenerable and the oxygen cycle needs to approach closure. We also discuss air revitalization systems for the International Space Station and needs for long-distance missions such as Mars transit.