Letters to the Editor

SUBJECT:  Cabin Air Quality
From:  Ken Murray <kmurray@shasta.com>

In a recent article [FAQ] you defended cabin air quality on commercial airlines as being better than the average commercial office building.  You referenced a Boeing article that stated, "Our airplanes typically provide ventilation of 13 to 20 cfm of air per occupant." [Boeing Forum Newsletter]

What, pray tell, does "typically" mean?  Does that indicate what airlines do or is it merely what they are capable of doing?

My own experience is that there are certain commercial air carriers I avoid, because every time I fly I get upper respiratory problems.  On other airlines, I never have this problem. 

Nader et. al. may be wrong in the focus of their attack, but I dare say there are many of us who believe some companies operate more "efficiently" at the expense of passenger comfort and health.  More outside air is the solution.  If it's too dry (and it is), install humidifiers.  Why doesn't the industry quit screwing around with the ASHRAE recommend standards?  Just adopt them as a minimum and install the perquisite humidifiers.  Is the solution unknown, or is it the bottom line?

EDITOR’S REPLY:

“What, pray tell, does "typically" mean?  Does that indicate what airlines do or is it merely what they are capable of doing?”

It means what actually happens on a “typical” flight.  The Boeing statement that "Our airplanes typically provide ventilation of 13 to 20 cfm [cubic feet per minute] of air per occupant,"  means the actual amount of cfm, per occupant, depends on two variables:  The particular model of aircraft used, and the percentage of seats occupied on any given flight.  The percentage of seats occupied is the biggest variable.  Worst case scenario (all seats occupied and an aircraft model that has the least efficient environmental control system – ECS), will still provide at least 13 cfm, per occupant.  Best case scenario, will provide 20 cfm.

“My own experience is that there are certain commercial air carriers I avoid, because every time I fly I get upper respiratory problems.  On other airlines, I never have this problem.”

Certainly, no one can know better than Mr. Murray how he feels after a given airline trip.  However, personal anecdotal experiences do not translate into reasonably certain knowledge as to causality.  The “rooster crowed and then the sun came up,” method of analysis (post hoc) is listed as one of the logical fallacies because it fails to account for the multitude of other variables that are involved in complex cause/effect analysis.  Emotions and/or feelings should never be treated as a valid tool of cognition.

“…some companies operate more "efficiently" at the expense of passenger comfort and health.”

I know of no studies that would validate this opinion.  Quite to the contrary, studies I have read seem to indicate that airline ECS technology has improved considerably in recent years.  See the Excerpts from the Flight Safety Foundation study on cabin air safety and disease transmission.

“More outside air is the solution.  If it's too dry (and it is), install humidifiers.  Why doesn't the industry quit screwing around with the ASHRAE recommend standards?  Just adopt them as a minimum and install the perquisite humidifiers.  Is the solution unknown, or is it the bottom line?”

Solution to what?  If in-flight cabin air is replaced more frequently and is of better quality than the air in schools, office buildings, buses, shopping centers, govt. offices, and our own homes, then how is the problem defined?

The point of the FAQ was that Nader mentalities manufacture crises that do not really exist.  They thrive on govt. subsidies and lawsuits for imaginary problems.  Such “consumer rights” activist organizations exist for the real purpose of siphoning off an ever-growing portion of what the rest of us have produced by the sweat of our brows.  Our society is made up of those who produce and those whose “work” amounts to figuring out how to forcibly take what others have produced.  The cabin air crisis is but one of many examples of the methodology of non-producers.

HUMIDIFIERS

I am opposed to increasing the humidity of in-flight cabin air for the following reasons:

·        Human Health.  It has not been shown that doing so would be beneficial to the health of passengers and crew.  Bacteria, fungi and molds can produce and aggravate human respiratory problems.  Increasing humidity enhances the ability of such organisms to thrive, survive and multiply to greater numbers.  That is why many doctors have for many years, advised patients with pulmonary respiratory problems, to move from high-humidity climates to those areas with very dry air, like Arizona.  Experienced joggers know that they must use moisture-reducing techniques in their footwear, to avoid being plagued with the “athlete’s foot” fungus. 

“The low humidity at altitude means that the moisture content in the air supply is also quite low. Relative humidities approximate those found in the U.S. southwestern deserts— commonly 10 percent to 20 percent. Such low humidities do not favor microbiological growth….The microbiologic flora [organisms] within an airline cabin under cruise conditions almost certainly cannot come from external air. Instead, [they are] supplied by the occupants and by those residual organisms present on cabin furnishings at the beginning of each flight.  The amount of contamination is relatively small. It is normally an order of magnitude less than that found on city buses and streets. … Microbiological concentrations appear to be related to [passenger] activity within the cabin.”  See FSF Report Excerpts

Thus, it would seem logical that adding more humidity to in-flight cabin air would result in more residual organisms being left on cabin furnishings after each flight and that, in turn, would increase the odds of those organisms surviving in greater numbers to infect more subsequent passengers. 

·        Costs. To install and maintain such units would be very costly, because they would have to meet regulatory standards, both to alter the airplane structure, and to provide acceptable designs.  Complying with the necessary paperwork is a very significant portion of regulatory costs.  Maintaining such equipment, to avoid buildup of dangerous microbes, would probably be very labor intensive.  Such expenditures, even if they were worth the investment, would further increase the cost of tickets so that even fewer of those in the lowest income quintile could afford to fly.  That, in turn, causes more to resort to auto travel and that increases the overall transportation fatality rate.

·        Safety.  All passenger airliners experience moisture-related problems that add to their maintenance costs. The main source of moisture is passenger respiration which results in condensation on the airplane skin. Moisture-related problems include "rain in the plane" (water dripping on passengers and crew), electrical equipment failures and wet insulation blankets.  It also creates the potential for structural corrosion.  Higher cabin humidity levels increase the rate of condensation; any moisture in that air will condense as the air moves over the cold structure. Boeing found that insulation blankets in a 737-300 airplane can contain up to 80 lb (36 kg) of water per airplane. Electrical equipment failures have been the direct result of condensation moisture. Dehumidification systems were considered by Boeing as one method of dealing with the damage that excess humidity imposes on aircraft structures, as they were very effective at removing moisture. However, that method was finally rejected because it was too costly.

I experienced a lengthy ground delay, before departing for Tokyo from LAX, when the preflight inspection revealed a failure in the primary pressurization control system.  All major components of that vital system were replaced, but the computer still enunciated the failure code.  Finally, one thoughtful mechanic suggested replacing the on/off control switch in the cockpit.  That solved the problem.  That switch, as all other switches in that cockpit, was subjected to excess humidity for a considerable period of time because Boeing had responded to crew complaints about “low air humidity” in the cockpit.  For the first time, Boeing made a cockpit humidifier an option to the airlines, when it built the 747-400.  Whether that humidifier actually helped reduce fatigue symptoms of cockpit crews, as claimed by some, is debatable because the only “evidence” is anecdotal experience.  What is certain knowledge, however, is that the extra humidity gradually caused the deposit of a thin film of a chalky white substance over the entire overhead electrical control panels in those cockpits, similar to the stuff that builds up on shower walls.  The defective pressurization control switch was so corroded from that substance (my conjecture is mineral deposits with possible microbial growth) that it culminated in a short circuit failure.  Since the other identical switch, that controlled the secondary backup system, was just as old, it too was replaced with a new one.

It is not too far-fetched to imagine a scenario where a B-747-400 is forced to ditch in the ocean because both pressurization control switches failed on the same flight, forcing the pilots to descend to 10,000 ft. so everyone could get enough oxygen to stay alive.  Flying at that altitude greatly increases the fuel consumption, per mile traveled.  That, in turn, would force the pilots to divert to the nearest emergency airport which could be a very long distance away, if the failure occurred in the middle of the Pacific Ocean.  In theory, they could make it to an emergency airport before running out of fuel, but if any other factors (bad weather, additional equipment failure, stronger winds than forecast, etc.) intervened, the result could be an ocean ditching.  For want of a shoe, the horse was lost…

Solutions to illusory airline safety “problems,” created by “consumer activist” groups who are grinding political axes, have a significant potential to harm us all.  When the public is inundated with press releases from groups that have a vested interest in more govt. regulation and lawsuits, we first need to ask the question “what kind of research data supports these claims of crisis?”  Then, if the data is indeed proved to be supportive and from credible and ethical sources, the next question is “what are the costs vs. benefits of the proposed solutions?  Will the cure cause other problems that are even worse?”  And finally, “will the proposed expenditure of limited safety dollars achieve a significant result (maximum lives saved per dollar spent), or could those limited safety dollars get ‘more bang for the buck’ if spent elsewhere?”  

Objective research, combined with dispassionate analysis is the only way to continually improve airline safety.  Using airline safety as a political football tends to have the opposite effect:  It operates in derogation of safety.

Additional information can be found at Boeing.  See also Facts and Myths.

July, 2000,  Revised February, 2001

Robert J. Boser    
Editor-in-Chief 
AirlineSafety.Com

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