Frequently Asked Questions
About ECHO Air for Aircraft

Question 1
It is stated that during normal cruise, ventilation air contaminants are removed at least in part. According to the patent this removal is only addressing contaminants coming either from the ventilation system or from the outside air which normally is quite clean. The contamination removal principles are not explained in detail. Principles like sorption, condensation, filtration, centrifugal and electrical forces are mentioned but not described.

During cruise the ECHO Air envelope ventilation system will remove contaminant gases and particulate in the ventilation air. Such contaminants might include:

  • Ozone,
  • VOCs from ingested hydraulic fluid or lubrication oil for example, which is lodged on the ventilation ducting from previous ingestion incidents,
  • Submicron particulate aerosols incidents, e.g., from ingestion of lubricating oil. (Incidents of ventilation ingestion of toxic aerosols allegedly causing health problems are currently a concern in some litigation cases.)

During cruise, ambient air should be relatively clean except perhaps for ozone. In addition to lowering levels of this gas in the ventilation air, ECHO air serves as a safeguard against any occasional aerosol ingestion incidents, and for removal of VOCs emanating in ventilation ducts to which such incident aerosols might have adhered.

Removal of gases will primarily be by absorption in specially selected anti-corrosion oil. Removal of particles will be by changes in flow direction (centrifugal forces) and filtration (media, electrostatic forces) of the ventilation air as it deflects off the skin and makes its way into the cabin through passageways between insulation blankets, panel cracks, etc.

Currently some of the cabin air is filtered through the envelope. This happens due to stack flows. Typically these flows enter from the cabin into the envelope at the crown and exit near the floor. With ECHO Air, only ventilation air is filtered through the envelope. The amount of air flowing through the envelope with the ECHO Air system may be less than currently flowing through the envelope unintentionally, and it may be cleaner. This will depend upon System set up objectives, equivalent leakage areas (ELAs) now and with ECHO Air, and the number and type of ventilation system ingestion incidents.

VOC exposures from engine oil and hydraulic fluid may not pose as much of an exposure hazard, if an ingestion incident of these fluids occurs as a fine aerosol transport. Some form of filtration safety measure may be required if occasional incidents are unavoidable. Use of ECHO Air for this purpose might be reasonable in that adequate ventilation line filtration may create large pressure losses.

The ECHO Air system will produce improved VOC sorption and lower VOC emission envelope characteristics over the current situation, benefiting cabin IAQ over the current situation. ECHO Air ventilation air filtration and VOC sorption will make ventilation air cleaner when it enters the cabin during cruise than is currently the case. As well, during ascent, ECHO Air envelope venting will expel VOCs from the envelope when their levels are most likely to be elevated with a warmer envelope. This contrasts with the current situation in which warm envelope VOCs freely enter into the cabin during ascent.

Question 2
In the patent it is said that the envelope ventilation air will flow through the insulation. This insulation is in blankets normally consisting of a fiber material covered by a plastic membrane. Does this insulation principle fit with the patent or do you need foam insulation? Use of aircraft insulation for air filtration causes:
  • Weight increase of the insulation,
  • Changed burn-through properties of the insulation material due to the contained contamination,
  • A slow destruction process of the insulation. After some years of in-service, insulation material would be found everywhere in the aircraft,
  • Etc.

  1. Sorption on solid surfaces
ECHO Air does not need an open polymer for sorption of VOCs. This new design does not rely on sorption on solid surfaces. Even if such does occur, it will be reversed at an appropriate stage of the flight by flushing out the envelope, thus minimizing any deleterious effects.
  1. Accumulation of ventilation versus cabin air particles in the envelope
Currently aerosols are collected in the envelope due to stack induced flows between the cabin and the envelope. In the ECHO Air system, aerosols will come from the ventilation air only. The amount deposited with ECHO Air may be less or more than the current situation depending upon factors noted earlier. ECHO Air provides a safeguard against exposure incidents to toxic submicron aerosols from, for example, lubricating oil ingestion in the ventilation system.

See also the Answer to Question 1

Question 3
What is the principle by which the cabin humidity is increased? According to the patent, this can only done by transportation of water into the cabin, which previously condensed on the structure or insulation.

Although a desirable goal for passenger comfort, humidification is currently not carried out in commercial aircraft due to safety and health considerations. Increasing humidity levels under the current design results in condensation on the airplane structure and skin during flight due to the cold ambient conditions at altitude. The ensuing condensation can lead to microbial growth, fungus and/or offgasing by damp materials provided moisture is not drained or evaporated.

Furthermore, with regard to safety aspects, condensation on the structure can cause corrosion, electrical problems and possible electrical smoke within the aircraft. To minimize these problems and protect the structural life of the fuselage, cabins should not be humidified in a conventional design.

In contrast, with the ECHO Air system condensation would not occur during cruise. Therefore:

  1. The above health and safety effects will not occur if the cabin is humidified during cruise.
  2. Cabin humidification will improve occupant comfort and any low-humidity related health effects now occurring.
  3. Cabin humidification can be at a rate that does not have to compensate for envelope condensation
Question 4
While the fire extinguishing aspect is attractive, the aircraft industry is focusing today more on passive means to improve aircraft in-flight fire safety, so how will this benefit be realized?

Having the ECHO Air option for combating a cabin fire allows designers and airlines to compare active and passive alternatives for achieving the best fire safety in the cabin and to make cost comparisons between alternate approaches to improving fire safety. The improved smoke venting function is inherent in the ECHO Air design, and can be realized at no additional cost. The fire suppressant injection capability of the ECHO Air system utilizes existing cargo fire suppressants and should not add substantially to the cost of an ECHO System installation.

Question 5
What is the benefit of the ECHO Air system compared to a system providing dried air between the structure and the insulation blankets?

The ECHO Air system does indeed supply dry air between the insulation blankets and the skin. It does this in the most cost, anti-corrosion and air quality-effective manner by:

  1. Reducing panel equivalent leakage areas (ELAs).
  2. Commissioned set up of System flows.
  3. Reducing stack pressure differences between the cabin and the envelope through use of envelope flow blockers.
  4. Using ventilation air on the way to the cabin rather than dehumidifiers.
  5. Ensuring humid cabin air does not enter the envelope through either convective air flow or diffusion.
  6. Reducing damp air entry into the envelope at times in the flight cycle when ventilation air may not be dry.
  7. Ensuring toxic and irritating envelope gases do not enter the cabin.
Question 6
Is it necessary to achieve envelope pressurization relative to the cabin to get the benefits of ECHO Air?

The ability to pressurize the envelope relative to the cabin throughout or vice versa (i.e. depressurize it throughout) is key. While putting ventilation air into the envelope will reduce cabin air entry into the envelope, it will not eliminate the moisture problem unless the envelope is pressurized relative to the cabin throughout (by say 1 Pa or more). To achieve this pressurization at low flows relative to minimum ventilation rate requirements (also a key), the cabin liner must be tight and flow blockers added.

Question 7
If the cabin were humidified during flight, we would then be relying on the ventilation system for structural integrity. Is that a good idea over the life of the airplane taking into account modifications that airlines make to interiors as well as deterioration in leakage paths, etc?

It is easy to check pressure differentials between the cabin and the envelope. Such differentials can be monitored automatically during flight and exceptions flagged. Our experience with the maintenance of pressure differentials in envelopes is that the envelope seal gets better with time as small particles fill the leakage area.

Question 8
Wouldn't humidifying the cabin air require a large water supply?

Cabin humidity drops below the minimum target of 40 percent SLE (sea level equivalent) at 23° C for avoiding health problems (e.g., asthma, mucous membrane irritation, and nasal drying leading to susceptibility to microbial infection) at ventilation rates above 2.5 CFM/person. Cabin humidity drops below the minimum comfort target cabin relative humidity (20 percent SLE) at ventilation rates above 5 CFM/person SLE.

To meet the 20% comfort criterion at 23° C, the humidification requirement is 0.033 litres/hour/person at a cabin ventilation rate of 10 CFM/person SLE. This translates to 20 litres or 44 pounds of water over a four hour, 150-passenger flight. To maintain the cabin at a 40 percent SLE relative humidity on such a flight would require 146 pounds of water. These amounts of water typically are available from the unused potable water carried on board.

Question 9
The aluminized Mylar used in current aircraft burns readily once a fire is started. If some Mylar is ignited, isn't this system more likely to lead to a conflagration?

With the ECHO Air system in place, an incipient fire is less likely to lead to a serious conflagration than in the current situation for a number of reasons:

  • The amount of air entering the envelope under normal cruise conditions need not be any more than currently entering the envelope and could be less if desired. This is because with ECHO Air, cabin liner panel continuity will be improved and stack flows will be reduced to make it easier to pressurize the envelope throughout. With our techniques, a 2000 square feet building envelope, for example, can be pressurized with as little as 10 CFM. Under ascent and descent conditions the amount of air entering the envelope will be even less.
  • Flow injection into the envelope with ECHO Air will be distributed at desired locations, remote from areas of potential ignition such as wiring for example. In contrast, under the current situation air enters the envelope randomly and primarily at the crown where most of the electrical wiring is located.
  • Localized air velocities from flow injectors can be reduced as desired by adding more injectors and using injector bonnets, distribution hoses, etc.
  • Envelope wiring will be in drier conditions and therefore less susceptible to electrical fires.
  • With ECHO Air, smoke sensors can be placed in the return air duct at each floor exhaust grille to quickly identify the presence and location of any smoke/fire incident, and switch to the envelope exhaust/cabin supply mode.
  • With ECHO Air, fire suppressants such as Halon can be injected into the envelope to extinguish a fire or incipient fire (i.e., smoldering) without creating a toxic cabin air situation.
Question 10
Will the system require a sophisticated flow controller, for example to cope with the relatively rapid changes in cabin/envelope pressure, density and temperatures during ascent and descent, to keep insulation dry, improve fire safety, etc.?

ECHO Air flow control settings are set when the ECHO Air System is installed and periodically adjusted if necessary, at C checks, for example. They are not controlled by in-flight envelope/cabin pressure differences.

During ascent, with ECHO Air, the cabin floor exhaust grille dampers are closed while the envelope is exhausted. Ventilation air flow distribution between the cabin and envelope can vary without any significant impact on envelope VOC and moisture flushing. With respect to fire safety, note that (1) smoke from any fire or pyrolysis incident will be flushed and (2) smoke detectors placed along the return air ducts will precisely locate its origin.

During descent, with ECHO Air the envelope is isolated air-wise from the cabin with the floor grille dampers open and all ventilation going to the cabin. The settings at this stage are optimal for envelope condensation control. If a fire is detected in the cabin or the envelope, then moisture condensation control is no longer the primary concern, of course. The smoke-flushing mode is entered and, if necessary, fire suppressant injected.