SOME OPERATORS HAVE EXPRESSED CONCERN ABOUT THE USE OF CHEMICALLY GENERATED SUPPLEMENTAL OXYGEN SYSTEMS BECAUSE OF THE MEDIA REPORTS SURROUNDING THE  INVESTIGATION OF THE DC-9 ACCIDENT NEAR MIAMI ON MAY 11, 1996.

The following information is offered to address those concerns and to explain some of the safety features inherent in the design of chemical oxygen generators.

Chemical oxygen generators are used on the majority of modern jet transport aircraft as a safety feature to supply supplemental oxygen in the event of a cabin depressurization. This safety device provides the emergency supplemental oxygen to passengers and cabin attendants during the descent following a loss of cabin pressure. With a loss of cabin pressure above about 15,000 feet, the oxygen compartment doors on the aircraft will open automatically, or manually as a backup. When the passenger or cabin attendant pulls the mask presented toward their face, a lanyard between the mask and the oxygen generator initiates the production of oxygen flow to the mask.

The chemical oxygen generators together with the required number of emergency oxygen masks are stored in latched oxygen mask compartments in one of the following locations depending upon the aircraft configuration: 1. Passenger Service Units overhead; 2. Passenger seat back units and; 3. Overhead oxygen
drop boxes. Similar configurations of oxygen generators and masks are provided for the lavatories, the cabin attendant seat locations, the purser stations and the crew rest modules.

Since the chemical process that produces the oxygen also produces heat (the surface temperature of the oxygen generator can reach 500ºF) a heat shield is installed to keep users from touching the hot surface.

Safety Features:
Scott Aviation Chemical Oxygen Generator Design Features:
· A stainless steel case of adequate strength to withstand four times the maximum operating pressure.
· Construction material and fabrication to prevent unit fragmentation or release of internal materials.
· Dual (redundant) pressure relief valves that minimizes the occurrence of unsafe internal pressure.
· Internal thermal insulation layers to avoid high temperature core material from contacting and burning through the outer housing and also control housing external temperature.
· An easily installed protective cap prevents inadvertent activation.
· The following placard is installed on all generators after late 1987:

WARNING
THIS UNIT GETS HOT.

WHEN REMOVING UNIT:
· INSTALL SAFETY CAP OVER PRIMER
· DO NOT PULL LANYARD
· IF ACTIVATED, PLACE ON SURFACE THAT WON'T BURN

Installation Aspects
· The heat shields prevent injury from touching the generator's hot surface.
· Only demonstrated compatible material are used in oxygen compartments.
· With more than 25 years of service life, the mounting design integrity confined it can withstand shock, acceleration, and vibration levels.

Summary of Handling Procedures:
· Oxygen generators are shipped as hazardous material to the aircraft manufacturers and distributors in Department of Transportation (DOT) approved shipping cartons. Note: The enclosed Federal Aviation Administration (FAA) AC No. 43-16 related to the transportation of chemical oxygen generators, notifies operators of the DOT Hazardous Materials Regulations change to prohibit the transportation of oxygen generators as cargo in passenger-carrying aircraft. This rule applies to both foreign and domestic aircraft entering, leaving, or operating in the United States (US) and/or to any person offering an oxygen generator for transportation on any of those aircraft.
· During handling at the aircraft manufacturer and at the PSU supplier, the safety cap is installed on the chemical oxygen generator primer.
· Aircraft manufacturer Maintenance Manuals (MM) and maintenance instructions require:
1. A "shipping cap" (safety cap) must be installed when removing an unexpended oxygen generator from its installed location.
2. Oxygen generators must be initiated and the chemical core fully expended before generator disposal.
3. Instruction on how to initiate and expend an oxygen generator.
4. Discussion of the hazardous materials contained in chemical oxygen generators give appropriate warnings relative to generator surface temperature upon activation.
5. Instructions for the disposal of expended chemical oxygen generators.

The US DOT requests that aircraft and oxygen generator manufacturers place the following placard on each generator, shipping paper, and package to facilitate compliance with the temporary ban on the shipment of oxygen generators (chemical) on passenger aircraft:

OXYGEN
GENERATOR
(CHEMICAL)

In addition, aircraft manufacturers were requested by the DOT to add a requirement to its service maintenance instructions that a retrofit label be applied to each generator now in service when it is accessed for repair or replacement. Douglas is in the process of complying with this DOT recommendation.

Operators are encouraged to review their flight and MM and training material to ensure the proper warnings are included. It is also necessary, to ensure safe use of the oxygen generators, for operators to follow the handling procedures referenced above. This is demonstrated by a review of several incidents which have resulted from improper handling of the generators. In one January 1986 case, maintenance personnel were removing oxygen generators during aircraft seat replacement, when approximately 35 oxygen generators were placed in a cardboard box without safety caps and with the lanyards still attached. Smoke was observed coming from the box which was removed from the aircraft and placed on the ramp. Flames were then observed in the box. Fire extinguishers were used to put out the flame.

In an August 1986 case, a fire occurred on a parked wide body aircraft at Chicago-O'Hare. The fire was thought to have started by an accidentally activated oxygen generator in a fly-away kit with flammable materials in the cargo compartment. The aircraft was destroyed. No injuries were reported. Following this incident, the FAA Office of Civil Aviation Security issued a telegraphic notice to all operators that chemical oxygen generators carried as replaceable spare components in fly-away kits or in a spare seat assembly in cargo compartments should be treated as hazardous materials.

The units contain sodium chlorate and are classified as an oxidizer, and should be securely stowed to prevent movement or boxed in appropriate packaging.

The FAA notice reminded operators that any spares meeting the definition of a hazardous material, if not required aboard their aircraft for its present operation, but being transported as company-owned material, must be transported in strict compliance with the provisions of Title 49, Code of Federal Regulations, Part 175.10(a)(2), or the International Civil Aviation Organization (ICAO) Technical instructions for the safe transport of dangerous goods by air, Part 1, Chapter 2, Paragraph 2.3.

In two other competitor aircraft cases, the passenger oxygen compartment had inadvertently opened at one location. The mask was apparently pulled by a passenger following the deployment, thus actuating the generator. In both cases, the flight attendant who apparently observed that no supplemental oxygen was needed, stowed the drop-down masks. The heat generated during activation of the oxygen generator caused the plastic hoses and masks to produce smoke and a strong burning smell coming from the compartments. The analysis of these events showed that this particular situation is not dangerous to the aircraft, but must be very unpleasant and frightening to the passengers and the crew. The Douglas Cabin Attendant Training Manual contains cautions regarding closing the oxygen generator compartment door once the generator is started. The affected passengers are relocated to other seats with functional supplemental oxygen generators.

There is another report of a chemical oxygen generator igniting its packing material following removal from its transport box. Analysis of this event revealed an unexpected actuation of the generator mechanism due to a loose firing mechanism release pin guide. Apparently, in this case, the firing mechanism release pin did not remain in position during unpacking which resulted in the activation of the oxygen generator. The report does not mention whether the safety cap was installed on the chemical oxygen generator primer in this particular unit. Inspection of the same batch of generators revealed that another four units were found in the same condition.

Finally, the National Transportation Safety Board (NTSB) reported the following facts relating to the DC-9 involved in the accident near Miami:

1. An intense forward cargo compartment fire occurred in flight just prior to the accident.
2. Chemical oxygen generators were packed in cardboard boxes without safety caps and placed in the forward cargo compartment before takeoff.

The NTSB investigation is on-going and no conclusions have been made as to the probable cause of the accident. Nonetheless, the danger of transporting chemical oxygen generators in this manner is apparent and led to the DOT ban.

THIS AOL IS FOR ADVISORY PURPOSES ONLY. NO FAA APPROVAL REQUIRED.