Jet aircraft have a range of up to 15,000km, enabling Airlines to operate non-stop flights lasting up to 17 hours cruising at 800 kilometers per hour, 40,000 feet above sea level.
The ability to connect distant continents and cities within hours makes aircraft a medium for transportation of vectors that transmit Chikungunya, Dengue, Filariasis, Malaria, Zika and Yellow fever to name but a few. As a preventive measure, aircraft must be disinsected to avoid spread of disease.
In order to ensure safety and comfort for extended periods in a confined environment at high speed and altitude, the aircraft cabin must be air-conditioned and pressurized.
How does disinsection, air-conditioning, pressurization and altitude affect passengers and crew?
International Civil Aviation Organization (ICAO) member states have an obligation under Annex 9 to the Convention on International Civil Aviation (Chicago Convention), to take effective measures to prevent the spread by means of air navigation of communicable diseases.
In addition, prevention of spread of diseases is an obligation for all World Health Organization (WHO) member states. Annex 5 of the WHO International Health Regulations (Specific measures for vector-borne diseases) states as follows;
“Every conveyance leaving a point of entry situated in an area where vector control is recommended should be disinsected and kept free of vectors”
Disinsection ensures that air navigation does not aid the spread of insect borne diseases transmitted by vectors like ticks, fleas, flies and mosquitoes. This also ensures that pests like cockroaches are kept at bay.
There are various ways of enforcing disinfection. In Uganda for instance, spraying of aircraft is a public health measure expressly provided for in the Aeronautical Information Publication. It states as follows;
“Pilots in command of aeroplanes arriving in Uganda from outside must make sure that their aeroplanes are sprayed before arrival and empty tins kept on board are surrendered to the health authority on arrival.”
Disinsection could either be pre-flight where the aircraft is sprayed before passengers are boarded, blocks-away where the aircraft is sprayed after passenger embarkation and door closure. It could be pre-flight and top of descent where the aircraft is, in addition to pre-boarding, be sprayed before arriving at its destination.
The residual method is also used, where all aircraft interior surfaces (ceilings, walls, carpets, baggage bins, galleys, toilets, crew rest rooms, cargo holds and wheel wells) are periodically sprayed and coated with a film of insecticide to ensure that potential disease carrying vectors or pests that may come into contact with the same are exterminated.
For blocks-away, preflight and top of descent methods, cabin crew walk along the aisle holding insecticide-discharging aerosol cans at luggage bin height. This is normally preceded by an announcement advising passengers to cover their faces in order to protect the eyes and nose until spraying comes to an end.
However, it is impossible to keep eyes closed or hold breath for more than 60 seconds to prevent respiratory exposure.
WHO recommended insecticides have d-phenothrin and permethrin as active ingredients. Whereas these synthetic man-made formulations are designed specifically to kill insects without affecting human health, exposure has been reported to have effects on cabin crew and passengers.
Dr. Aldoub (Aircraft Disinsection, 2005) makes reference to reports completed by flight attendants that highlight effects on passengers and crew following pyrethroid application. Metallic taste, slight and non-specific irritation of the eyes, throat, skin and upper respiratory tract, cough, asthma, headache and allergic reactions were mentioned in the reports.
Van Netten (Analysis and Implications of Aircraft Disinsectants, 2002) states;
“It is known that aerosolized pesticides can trigger a ‘non-specific’ asthmatic response, i.e. broncho-constriction and respiratory symptoms (WHO, 1995). The synthetic pyrethroid sprays are not considered to be allergenic (WHO, 1995) and until recently, there was no evidence that a non-asthmatic can become sensitized after exposure to aerosolized synthetic pyrethroid insecticides. One case describing such a response to tetramethrin has now been documented (Vandenplas et al., 2000)”
The American Journal of industrial Medicine (May 2007) published information regarding pesticide illness among flight attendants due to aircraft disinsection. The information was based on 17 reports of illness involving flight attendants exposed to pesticides following disinsection. In was determined that aerosol application of a pesticide in the confined space of an aircraft cabin poses a hazard to flight attendants.
The International Air Transport Association (IATA) has stated in its 2017 Medical Manual;
Despite safety assurances from WHO, disinsection and its effect on passengers and crew is still a matter of concern.
Air-Conditioning and Pressurization
Aircraft cabins have an airtight design for safety and comfort. The safety aspect is to provide oxygen which is in low supply because of thin air at high altitude. The comfort aspect is to cushion passengers and crew against the noise generated by jet engines and air as it rushes past the airframe at speeds in excess of 800kph.
Atmospheric pressure has various units of measurement; atmosphere (atm), pounds per square inch (psi), inches of mercury (hg), hectopascals (hpa), millibars (mbar) and millimeters of mercury (mm Hg).
1 atm=14.7 psi=29.92 Hg=1013.25 hpa=1013.25 mbar=760 mm Hg.
An increase in altitude leads to a decrease in atmospheric pressure and temperature as illustrated below;
Source: Manual of the ICAO Standard Atmosphere.
There is more oxygen pressure at sea level than at altitude. This allows oxygen to be absorbed into the bloodstream with ease as pressure pushes it from the lungs into the bloodstream. When the altitude exceeds 7000 feet above sea level, low oxygen pressure means less oxygen is pushed into the bloodstream. If not addressed oxygen deprivation could lead to hypoxia, loss of consciousness and death.
The table below shows how oxygen pressure in the atmosphere decreases with increase in altitude.
According to Wolff (Cabin decompression and Hypoxia, 2006) increase in altitude lowers the time of useful consciousness. If pressurization is lost at 15,000 feet above sea level, humans can remain conscious for 30 minutes.
At 30,000 feet consciousness can only be maintained for 3 minutes while at 50,000 feet, a human being will remain conscious for only 9 seconds.Source: FAA Cabin Environmental Control Systems; Physiology of flight.
In order to ensure the survival of passengers and crew, the aircraft cabin is made to “climb” to an altitude not exceeding 8000 feet above sea level. This is done by the environmental control and pressurization system which taps hot air off the engine(s), cools it, supplies the same through temperature controlled air ducts to different zones in the cabin and releases some in a controlled manner through an outflow valve.
The cabin altitude must be maintained at 8000 feet or lower, regardless of the aircraft’s cruising altitude. This controlled cabin environment protects passengers and crew from the extreme temperature and pressure levels at altitude, ensuring comfort during flight. It also ensures there is sufficient air and pressure in the cabin for normal breathing and oxygen circulation.
Although intended to be subtle, pressurization changes in the aircraft cabin during climb or descent can be felt in the ears. Discomfort, muffled hearing and pain experienced by passengers are attributed to pressure distortion between the inner and outer ear as the cabin pressurizes of depressurizes.
Passengers are advised to swallow, yawn or use the Valsalva maneuver to clear their ears, effectively restoring pressure between the inner and outer ear.
Annex 6 to the Chicago Convention, requires pressurized aircraft intended to be operated at flight altitudes at which the atmospheric pressure is less than 376 hpa (25,000 feet) to be equipped with a device to warn the flight crew in the event of loss of pressurization. A sufficient quantity of stored breathing oxygen should be available to passengers and crew, to enable them breathe during emergency descents to an altitude where the atmospheric pressure permits breathing without the aid of supplemental oxygen.
Loss of pressurization can be fatal. The crash of Helios flight 522 in 2005 was attributed to pilots’ failure to identify loss of pressurization. Subsequently, they were incapacitated and the plane flew on auto pilot until it run out of fuel and impacted the ground, killing all 121 passengers and crew.
Although intended to create a comfortable environment for passengers and crew at altitude, air conditioning and pressurization have a downside.
Air at altitude has a low humidity and moisture content. As a result, cabin air has a low moisture content. To increase humidity, cabin air is recycled and mixed with fresh air from outside the cabin to introduce humidity and moisture.
IATA (Medical Manual, 2017) states that even with good load factors, cabin humidity varies between 10 and 20 percent;
“While 10-20 % of relative humidity is not ideal, it does not seem to have a significant impact on the occupants’ health. A study on the subject was published by the Royal Air Force Institute of Aviation Medicine in England and they concluded that it was unlikely that the low level of relative humidity found in aircraft cabin had any long and short term ill effects, if overall hydration is maintained. However, it is certainly accepted that low levels of relative humidity may affect passenger and crew comfort by superficial dehydration. Dry, itchy or irritated eyes, dry stuffy nose, dry throat and skin dryness are among the common complaints.”
Although the artificial cabin maximum altitude is designed to increase atmospheric pressure to allow passengers and crew breathe comfortably, the heart works harder at altitude than it does at sea level. Below 7000 feet above sea level, the heart in a young healthy individual may cope with increased workload. This may not be the case for passengers of middle or advanced age.
In 2006, the Australian Transport Safety Bureau (ATSB) conducted an analysis of in-flight passenger injuries and medical conditions, to determine the most common in-flight medical problems in passengers and what proportion of these problems resulted in an aircraft diversion.
The analysis revealed that 44% of inflight deaths on Australian registered aircraft between 1st January 1975 and 31st March 2006 were caused by heart attack. During the same period, 35% of medical conditions that led to aircraft diversions were heart attacks.
The ATSB compared its findings with reports from the United States of America, France, Korea and United Kingdom and stated;
“It is therefore clear that from an analysis of these studies the most serious medical events occurring in passengers in-flight are cardiac (chest pain or heart attack) neurological (fainting, fitting or dizziness) and respiratory problems. The results of the present study involving Australian Civil Aviation passengers are certainly consistent with this international experience.”
The ATSB report made reference to data on inflight deaths that occurred worldwide between 1977 and 1984 provided to IATA by 120 of its member airline and concluded;
“Most of the in-flight deaths were in middle aged men with 77 per cent apparently not suffering from any health problems prior to travel. The results showed an annual in-flight death rate of 72 deaths per year. The majority (56 per cent) of the in-flight deaths were due to heart disease, which is consistent with the findings of the present study, in which heart disease accounted for majority of in-flight deaths.”
The ATSB study suggests that preflight medical screening may reduce the incidence of in-flight medical events. However, there are incidents of pilots-who are routinely screened-suffering heart attacks during flight. The literature reviewed by this author reveals that all the pilots were middle aged men not suffering from any health problems prior to their assigned duty.
The consistent findings are not a mere coincidence. Hopefully, scientists can provide answers as to why more men succumb to heart disease during flight.
Passenger jet aircraft cruise at altitudes between 30,000 and 41,000 feet above sea level. Business jets can cruise at 51,000 feet. Before being decommissioned, Concorde was able to achieve and maintain a cruising altitude of 60,000 feet above sea level.
Aircraft fuselage are subjected to less drag because of thin air molecules and low air density at high altitude. An aircraft at high altitude burns less fuel for a given airspeed than it does for the same speeds at low altitude. Less drag means less power is needed to propel the aircraft.
In addition, flying high above the clouds ensures that aircraft avoid bad weather, storms and turbulence during cruise, ensuring passenger comfort.
Finally, from a safety perspective, jets cruising at speeds in excess of 800 kph stay clear of obstacles like trees, mountains, helicopters and hot air balloons above 35,000 feet. Separation from other aircraft is provided by air traffic control units and onboard collision avoidance systems. This allows pilots to fly passengers quickly to their destinations without having to worry about obstacles or other aircraft.
Unfortunately and unknown to most passengers, a danger invisible to the naked eye lurks high up above the earth’s surface.
This is ionizing radiation in outer space formed by charged energy protons. It is measured in milliSieverts (mSv). Exposure depends on altitude, latitude and duration. There is more ionizing radiation at high altitudes and further away from the equator due to a higher concentrations of protons at the poles. Passengers on long flights at high altitudes and closer to the poles are exposed to a higher dosage of cosmic radiation.
Under Annex 6 to the Chicago Convention, it is mandatory for all civilian passenger aircraft intended to be operated above 49,000 feet to be fitted with equipment that measures and continuously indicates to crew members, the dose rate of total cosmic radiation being received and the cumulative dose on each flight.
The operations manual for such aircraft must have information to enable the pilot determine the best course of action in case of exposure to cosmic radiation and procedures in the event that a decision is taken to descend, with or without air traffic control clearance.
In addition to the mandatory requirements of Annex 6, ICAO member states must have regulations in place to regulate high altitude aircraft operations, and spell out obligations of the airline vis-à-vis crew and passengers.
In Uganda, for instance, the Civil Aviation (Operation of Aircraft) Regulations require operators with flight operations at or above 49,000 feet to;
The European Council Basic Safety Standards (Directive 96/29) on protection of aircrew is similarly worded, with the following additions;
When ionizing radiation passes through the body and energy is transmitted to the tissues, it may affect atoms within individual cells and result in a variety of health risks including development of cancer and risk to the health of a foetus. For an accumulated dose of 5 mSv per year over an exposure period of 20 years, there is a 0.4% likelihood that one will develop cancer. Similarly, exposure of the foetus for 80 hours for a month increases the risk of damage by between 1 in 6,000 and 1 in 30,000 depending on the route flown (IATA Medical Manual, 2017).
Whereas the likelihood of getting cancer is very low. IATA emphasizes that there is no threshold below which exposure is completely safe. More studies are being conducted and hopefully, additional information may be available in the future.
The possible effects of cabin conditions on passengers and crew highlighted above are rare and only likely to affect people who are either allergic, hyper sensitive, or have pre-existing medical conditions.
Prudence requires that passengers planning to travel by air visit their physicians for assessment. The airline’s duty is to ensure safety and cannot be held responsible for injury or death resulting from pre-existing conditions, because it neither has the means to know, nor a duty to ensure that all passengers are fit for flight. Disclosure of known medical conditions could assist airlines determine whether or not to accept passengers for travel, or possibly guide passengers on how to manage their conditions.
Just like other means of transport, passengers voluntarily assume risk when they opt for air transport as their preferred mode of travel.
Despite the cabin perils-which have been known for several decades, air travel is still a lot safer and convenient. Alternative modes like road, rail and sea are not only inconvenient, they too have associated perils. For now, the benefits associated with jet aircraft and air travel outweigh all known risks.