question: what does the bag that doesn’t inflate on airplane oxygen masks actually do?
comment: It’s called a non-rebreather reservoir mask. In hospitals it’s also called a trauma mask. It comprises of a mask and a bag attached. There is a series of one way valves between the mask and bag and also on the side of the mask (which are really only flaps of flimsy plastic). Oxygen flows from the source, into the bag, and then up into the mask. Ideally, before use you should occlude the valve between the mask and bag in order to fill the bag with oxygen (the reservoir). Then you should attach the bag tightly to your face to minimise any gaps between your face and the mask. When you then inhale, the valves on the sides of the mask close and the valve between the bag and mask opens. Thus you inhale a high concentration of oxygen from the bag. When you exhale, the opposite happens. The valve between the mask and bag closes and the valves on the side of the mask open. Thus you exhale out of the sides of the mask, and not into the bag (thus you do not rebreathe the same gas in and out of the bag over and over, hence the name non-rebreather). While you are exhaling, the bag is refilling with oxygen from the wall. With a full bag of oxygen and a tight seal they say you can get up to 85% oxygen in every breath. If you do not inflate the bag, you are only getting what’s coming out from the source. I’ve no idea what the oxygen flow rate is on a plane but in a hospital this is about 15L per minute. This sounds like a lot but when you consider that an average breath in an emergency might be easily 1-2 L, inhaled over half a second, you can see that the peak inspiratory flow rate is about 120-240L per minute. The oxygen source is not delivering the oxygen fast enough to provide this breath as pure oxygen. What happens is that you entrain air through the gap between your face and the mask. During cabin decompression this air will have very little oxygen, and you will probably become hypoxic and pass out pretty quickly unless a rapid descent is made in order to repressurise the cabin. Long story short, you really should inflate the bag with oxygen first in order for the mask to work, but it’s far too complicated for the average person to learn how to do this in an emergency. In reality it’s a token effort which might be enough to keep you alive but unconscious until a descent is made.
passages: The modification process generally lowers the amount of oxygen (O) in the headspace of the package. Oxygen can be replaced with nitrogen (N), a comparatively inert gas, or carbon dioxide (CO).
  
  A stable atmosphere of gases inside the packaging can be achieved using active techniques, such as gas flushing and compensated vacuum, or passively by designing “breathable” films.
  
  Section::::History.
   Three main kinds of oxygen masks are used by pilots and crews who fly at high altitudes: continuous flow, diluter demand, and pressure demand.
  
  In a "continuous-flow system", oxygen is provided to the user continuously. It does not matter if the user is exhaling or inhaling as oxygen is flowing from the time the system is activated. Below the oxygen mask is a rebreather bag that collects oxygen during exhalation and as a result allows a higher flow rate during the inhalation cycle.
   Section::::Complications.:Stomach inflation / lung aspiration.
   During the final sealing process, the bag may be filled with air from a blower or from an inert gas supply such as nitrogen. Inflating the bag helps reduce the crushing of fragile products such as potato chips, while inflating with inert gas helps drive out oxygen and retards the growth of bacteria that would spoil the product. Other product finishes such as hole punching for retail hanging racks will be done concurrently or just after the "Top Seal" is made.
   A rudimentary type of mechanical ventilator device that has the advantage of not needing electricity is a flow-restricted, oxygen-powered ventilation device (FROPVD). These are similar to manual resuscitators in that oxygen is pushed through a mask to force-inflate the patient's lungs, but unlike a manual resuscitator where the pressure used to force-inflate the patient’s lungs comes from a person manually squeezing a bag, with the FROPVD the pressure needed to force-inflate the lungs comes directly from a pressurized oxygen cylinder. These devices will stop functioning when the compressed oxygen tank becomes depleted.
  
  Section::::Types of manual resuscitators.
   Currently the only devices that can deliver pre-set, physician-prescribed inflation volumes reliably within safety guidelines are mechanical ventilators that require an electrical power source and/or a source of compressed oxygen, a higher level of training to operate, and typically cost hundreds to thousands of dollars more than a disposable manual resuscitator.
  
  Section::::Additional components / features.
  
  Section::::Additional components / features.:Filters.
  
  A filter is sometimes placed between the mask and the bag (before or after the valve) to prevent contamination of the bag.
  
  Section::::Additional components / features.:Positive end-expiratory pressure.
  
  Some devices have PEEP valve connectors, for better positive airway pressure maintenance.
   BULLET::::- that even though oxygen will be flowing to the mask, the plastic bag may not inflate (required in the United States after a woman fatally removed her mask thinking it was not working); some planes such as the Boeing 787 or Boeing 777-300ER do not include plastic bags in the oxygen masks.
  
  BULLET::::- if applicable to the aircraft in question, that the passenger must pull down on a strap to retrieve the mask
   Some bags are designed to collapse for storage. A bag not designed to store collapsed may lose elasticity when stored compressed for long periods, reducing its effectiveness. The collapsible design has longitudinal scoring so that the bag collapses on the scoring "pivot point," opposite to the direction of normal bag compression.
  
  Section::::Manual resuscitator alternatives.
   Oxygen scavenger
  
  Oxygen scavengers or oxygen absorbers are added to enclosed packaging to help remove or decrease the level of oxygen in the package. They are used to help maintain product safety and extend shelf life.
  
  There are many types of oxygen absorbers available to cover a wide array of applications.
   Section::::Oxygen control.
  
  Oxygen scavengers or oxygen absorbers help remove oxygen from a closed package. Some are small packets or sachets containing powdered iron: as the iron rusts, oxygen is removed from the surrounding atmosphere. Newer systems are on cards or can be built into package films or molded structures.
  
  In addition, the physical characteristics of the packaging itself (oxygen transmission rate - OTR) can dictate how effective an oxygen absorber can be, and how long it will stay effective. Packaging with a low OTR will let less oxygen in the closed package through the polymer barrier itself.
  
  Section::::Atmosphere.
   For modern military aircraft such as the United States’ F22 and F35, both of which have operational altitudes of or more, the pilot wears a "counter-pressure garment", which is a gsuit with high-altitude capabilities. In the event the cockpit loses pressure, the oxygen system switches to a positive-pressure mode to deliver above-ambient-pressure oxygen to a specially sealing mask as well as to proportionally inflate the counter-pressure garment. The garment counters the outward expansion of the pilot’s chest to prevent pulmonary barotrauma until the pilot can descend to a safe altitude.
  
  Section::::See also.
  
  BULLET::::- Altitude sickness
   People who climb mountains or fly in non-pressurized fixed-wing aircraft sometimes have supplemental supplies. Pressurized commercial airplanes have an emergency supply of automatically supplied to the passengers in case of cabin depressurization. Sudden cabin pressure loss activates chemical oxygen generators above each seat, causing oxygen masks to drop. Pulling on the masks "to start the flow of oxygen" as cabin safety instructions dictate, forces iron filings into the sodium chlorate inside the canister. A steady stream of oxygen gas is then produced by the exothermic reaction.
   EFB users and installers should be aware of recent, clarified guidance for FAA Inspectors. Draft guidance pertaining to EFB operational authorization and airworthiness/certification requirements is maintained by the FAA.
  
  Clarifying the intent of FAA Advisory Circular AC 120-76A, new draft inspector handbook guidance includes the following requirements:
  
  BULLET::::- PEDs used in a Class 1 or Class 2 configuration must meet the rapid decompression testing requirements of standard RTCA DO-160E.
  
  BULLET::::- Any data connectivity of PEDs used in a Class 1 or Class 2 configuration to aircraft systems shall be performed in accordance with a Supplemental Type Certificate, Type Certificate or Amended Type Certificate.
   This method of triple bagging creates an airtight environment, and seals any insects present in the crop inside the bag. These insects briefly continue to consume oxygen, but as oxygen levels in the bags drop, and CO concentrations rise, the insects stop feeding and quickly die, thereby protecting the crop from further damage.
   BULLET::::- ValuJet Flight 592 (1996)- expired chemical oxygen generators were improperly prepared and labelled as company material and without being designated as HAZMAT and placed in the cargo hold of a passenger aircraft, where they caught fire in flight resulting in a crash that killed all 110 persons onboard
   A hypoxic, carbon dioxide free metabolically inert gas is provided for inhalation by confining the gas supply and the head in an impermeable bag which prevents contamination with oxygen from the surrounding air, minimising the amount of gas required. (The same effect could be reached by flooding any enclosed space with the gas, but much more gas would be needed, and this would be hazardous to a third party entering the space, an effect which is well known as a cause of industrial fatalities.)
   Bag and valve combinations can also be attached to an alternative airway adjunct, instead of to the mask. For example, it can be attached to an endotracheal tube or laryngeal mask airway. Small heat and moisture exchangers, or humidifying / bacterial filters, can be used.
   Today there are several manufacturers of self-inflating bag resuscitators. Some, like the original Ambu bag, are durable and intended for reuse (after thorough cleaning). Others are inexpensive and intended for a single use.
  
  Initially produced in one size, now BVMs are available in sizes for use with infants, children or adults.
  
  Section::::Standard components.
  
  Section::::Standard components.:Mask.
   Section::::Practical information.
  
  In order to increase the effectiveness of PICS bag technology, the following suggestions should be considered:
  
  As studies show, PICS bags work not only by depriving bruchids of oxygen, but also by dehydrating their environment. Therefore, this technology could be improved by finding additional methods of quickly lowering the moisture content within sealed bags.
   Self-rescuers are small, lightweight belt or harness-worn devices, enclosed in a rugged metal case. They are designed to have a long service life of around 10 years (longer for shelf storage) and to be worn every day by each miner. Once used, they have a working life of a few hours and are discarded after opening.
  
  There are two forms of rescuer: respirators and oxygen sources.
  
  Section::::Respirators.
   Unlike the inerting systems on military aircraft, this inerting system would run continuously to reduce fuel vapor flammability whenever the aircraft's engines are running; and its goal is to reduce oxygen content within the fuel tank to 12%, lower than normal atmospheric oxygen content of 21%, but higher than that of inerted military aircraft fuel tanks, which is a target of 9% oxygen. This is accomplished by ventilating fuel vapor laden ullage gas out of the tank and into the atmosphere.
  
  Section::::Aircraft.:FAA rules.
   In reverse pulse-jet baghouses, individual bags are supported by a metal cage (filter cage), which is fastened onto a cell plate at the top of the baghouse. Dirty gas enters from the bottom of the baghouse and flows from outside to inside the bags. The metal cage prevents collapse of the bag.
   Commercial aircraft provide emergency oxygen to passengers to protect them from drops in cabin pressure. Chemical oxygen generators are not used for the cockpit crew, who are typically supplied using compressed oxygen canisters also known as oxygen bottles. In narrow body airliners, for each row of seats there are overhead oxygen masks and oxygen generators. In some wide-body airliners, such as the DC-10 and IL-96, the canisters and oxygen masks are mounted in the top portion of the seat backs, since the ceiling is too high above the passengers. If a decompression occurs, the panels are opened either by an automatic pressure switch or by a manual switch, and the masks are released. When the passengers pull down on the mask they remove the retaining pins and trigger the production of oxygen.
   The BVM consists of a flexible air chamber (the "bag", roughly a foot in length), attached to a face mask via a shutter valve. When the face mask is properly applied and the "bag" is squeezed, the device forces air through into the patient's lungs; when the bag is released, it self-inflates from its other end, drawing in either ambient air or a low pressure oxygen flow supplied by a regulated cylinder, while also allowing the patient's lungs to deflate to the ambient environment (not the bag) past the one way valve.
  
  Section::::Standard components.:Bag and valve.
   Reference: FAA Advisory Circular AC 120-76D, EASA Acceptable Means of Compliance AMC 20-25, ICAO Document 10020 "EFB Manual" and FAA Order 8900.1 Inspector Handbook (esp. Vol 4 Chap 15) for the most recent and accurate descriptions:
  