Passenger Supplemental Oxygen - Oxygen Systems - Airframes & Aircraft Systems #55

Summary

This lesson explores the supplemental oxygen systems for passengers and cabin crew on airplanes. It discusses the continuous flow type systems, the storage of masks in passenger service units, and the automatic/manual deployment mechanisms. The lesson also covers two types of oxygen supply systems: high-pressure gaseous and chemical generator systems. It details the operation of chemical oxygen generators, their maintenance needs, and safety precautions. The script emphasizes regulations for oxygen mask availability and the oxygen flow process during emergencies.

Takeaways

• 🌐 The lesson discusses the oxygen systems for passengers and cabin crew on airplanes.
• 🔄 The supplemental oxygen supply is of the continuous flow type, ensuring a constant supply regardless of usage.
• ✈️ On some smaller aircraft, the flight deck may also use a continuous flow system for oxygen supply.
• 💨 The oxygen masks are stowed in passenger service units and are automatically deployed when the cabin altitude reaches 14,000 feet or can be manually deployed by the flight crew.
• 🔗 There are two methods for automatic door actuation in the gaseous system: pneumatically by oxygen pressure or electrically by solenoids in systems with chemical generators.
• 📏 Regulations mandate that aircraft operating above 25,000 feet must have 10% more oxygen masks than the number of cabin seats.
• 🛫 Oxygen enters the mask through a rebreather bag, where it mixes with exhaled air and cabin air, but it does not protect against noxious fumes.
• 🔧 A high-pressure gaseous oxygen supply system is similar to the CRU system but uses mass connection points instead of demand regulators.
• 🔬 Chemical oxygen generators are used on most modern aircraft; they are light, inexpensive, and virtually maintenance-free.
• ⏱️ When ignited, the chemical reaction in the generator produces heat and releases oxygen, which is then filtered and regulated to a safe temperature and pressure for breathing.

Q & A

What type of oxygen systems are provided for passengers and cabin crew in an aircraft?

The aircraft provides continuous flow type oxygen systems for passengers and cabin crew.

How does the oxygen supply system differ between high-pressure gaseous systems and chemical generator systems?

In high-pressure gaseous systems, the oxygen masks are stowed in passenger service units that open automatically by a barometric release mechanism, while in chemical generator systems, the masks are also stowed in service units but are opened by electrical solenoids.

What triggers the automatic opening of the oxygen mask doors in the passenger service units?

The doors open automatically if the cabin altitude reaches 14,000 feet or by manual selection by the flight crew at any altitude.

How does the oxygen flow initiate when a passenger pulls the mask towards their face?

Pulling the mask towards the face pulls a cord which either opens a check valve in the gas supply system or operates an electrical or percussion cap firing mechanism on the chemical generator, initiating the oxygen flow.

What is the regulation for the number of oxygen masks required on aircraft intended to be operated above 25,000 feet?

The number of masks must exceed the number of cabin seats available by 10%, with the extra masks spread evenly throughout the cabin.

How does the oxygen enter the mask and what does it mix with before being inhaled by the passenger?

The oxygen enters the mask through a plastic rebreather bag, where it is mixed with exhaled air and cabin air.

Why don't passenger oxygen masks provide protection from noxious fumes?

Passenger oxygen masks don't provide protection from noxious fumes because they mix the oxygen with cabin air, which could contain such fumes.

How does a high-pressure gaseous oxygen supply system differ from a chemical oxygen generator system?

In a high-pressure gaseous oxygen supply system, demand regulators are replaced by mass connection points with valves operated by mass cords, and there is also a flow control valve that can be opened automatically by a barometric switch or manually by a flight deck switch.

What are the main components of a chemical oxygen generator used in aircraft?

A chemical oxygen generator consists of a charge block made of sodium chlorate and iron powder, surrounded by filter material and thermal insulation, all housed in a cylindrical case.

How long does a chemical oxygen generator typically burn and what is its oxygen output?

A chemical oxygen generator burns at a temperature of approximately 200 degrees Celsius for a minimum of 15 minutes, releasing about 45% of its weight as usable oxygen.

How does a relief valve in a chemical oxygen generator system function?

A relief valve prevents the internal pressure in the generator from exceeding 50 psi, ensuring the safety of the system.

Outlines

00:00

🌐 Aviation Oxygen Systems Overview

This paragraph discusses the different types of oxygen systems available for passengers and cabin crew on aircraft. It explains the continuous flow system, where oxygen flows regardless of whether it's being breathed. The text also covers the two types of systems used on smaller aircraft: high-pressure gaseous systems and chemical generator systems. Oxygen masks are stored in passenger service units and are deployed automatically or manually. The paragraph further explains the automatic door actuation methods and the process of oxygen flow initiation. It also touches on regulations requiring an excess of masks for aircraft operating above 25,000 feet and the functionality of high-pressure gaseous oxygen supply systems. The discussion includes the characteristics and maintenance requirements of chemical oxygen generators, which are prevalent in modern aircraft due to their light weight and low maintenance needs.

05:00

🔥 Chemical Oxygen Generation and Safety

Paragraph 2 delves into the specifics of chemical oxygen generators, which are used to supply oxygen in the event of a cabin depressurization. It describes the chemical reaction involving sodium chlorate and iron powder that occurs when the mask is pulled down, igniting a charge block and releasing oxygen. The paragraph outlines the temperature and duration of the burn, as well as the oxygen output compared to the requirements during an emergency descent. It also mentions the safety features of these generators, such as a relief valve to prevent excessive pressure and a heat-sensitive indicator to signal when the generator needs replacement. The summary concludes with a reiteration of the automatic deployment of oxygen masks when cabin altitude exceeds 14,000 feet and the composition of the air breathed through passenger masks.

Keywords

💡Supplemental Oxygen

Supplemental oxygen refers to the additional oxygen provided to passengers and crew in an aircraft when the normal atmospheric oxygen levels are insufficient, typically during a cabin decompression. In the context of the video, supplemental oxygen is crucial for ensuring safety and is delivered through a continuous flow system, ensuring a steady supply regardless of whether it is being breathed or not.

💡Continuous Flow Type

The continuous flow type system is a method of oxygen delivery where oxygen is supplied at a constant rate. As mentioned in the script, this system ensures that once the flow to a mask is initiated, it continues without interruption, which is vital during emergencies where a reliable oxygen supply is necessary.

💡High Pressure Gaseous System

A high-pressure gaseous system is a type of oxygen supply system that uses stored oxygen in a high-pressure tank. The script explains that this system can be used to supply oxygen to cabin crew and passengers, and it operates by releasing oxygen through a demand regulator when a mask is in use.

💡Chemical Generator System

A chemical generator system produces oxygen through a chemical reaction, typically using a mixture of sodium chlorate and iron powder. The script highlights that these generators are used in modern aircraft due to their light weight, low cost, and minimal maintenance requirements. They are activated by pulling a mask down, which triggers the chemical reaction to produce oxygen.

💡Passenger Service Unit (PSU)

The Passenger Service Unit is a storage compartment located above passenger seats, which contains oxygen masks and other safety equipment. The script describes how the doors of these units open automatically when the cabin altitude reaches 14,000 feet or can be manually opened by the flight crew, deploying the oxygen masks for use.

💡Barometric Release Mechanism

A barometric release mechanism is a device that uses changes in air pressure to trigger actions, such as opening the doors of a PSU. The script explains that this mechanism is used to automatically deploy oxygen masks when the cabin altitude reaches a certain level, ensuring rapid access to oxygen in the event of a decompression.

💡Cabin Altitude

Cabin altitude refers to the altitude equivalent of the air pressure inside the aircraft cabin. The script mentions that oxygen masks are automatically deployed when the cabin altitude reaches 14,000 feet, indicating a significant drop in cabin pressure that necessitates supplemental oxygen.

💡Rebreather Bag

A rebreather bag is a component of the oxygen mask system that collects exhaled air and mixes it with fresh oxygen and cabin air. The script explains that the oxygen entering the mask is mixed in this bag, which helps to conserve oxygen and regulate the breathing cycle for the user.

💡Chemical Oxygen Generator

A chemical oxygen generator is a device that produces oxygen chemically, often used in aircraft for emergency oxygen supply. The script provides a detailed description of how these generators work, including the composition of the charge block and the process of ignition, which is critical for understanding the operation of the oxygen supply system in an emergency.

💡Oxygen Mask Deployment

Oxygen mask deployment refers to the process of making oxygen masks available to passengers and crew in an aircraft. The script describes how masks are stowed and how they are automatically presented to users when the cabin altitude exceeds a certain threshold, which is a critical safety feature in aircraft design.

💡Noxious Fumes

Noxious fumes are harmful gases that can be present in certain environments, including in an aircraft cabin during a decompression event. The script notes that while oxygen masks provide oxygen, they do not protect against noxious fumes, which is an important consideration in the design of aircraft safety systems.

Highlights

Supplemental oxygen systems for passengers and cabin crew are examined.

Regulations for the use of supplemental oxygen in aircraft are discussed.

Passenger and cabin attendant oxygen is supplied via a continuous flow system.

Smaller aircraft may use a continuous flow system in the flight deck.

Oxygen supply can be from high-pressure gaseous systems or chemical generators.

Oxygen masks are stowed in passenger service units above seats.

Doors of service units open automatically at 14,000 feet or by manual selection.

Two methods of automatic door actuation are used in gaseous systems.

Chemical generators use electrical solenoids for door opening.

Masks drop to a half-hung position and initiate oxygen flow when pulled.

Regulations require extra oxygen masks for aircraft operating above 25,000 feet.

Extra masks must be evenly distributed throughout the cabin.

Passenger masks don't protect from noxious fumes due to cabin air mixing.

High-pressure gaseous oxygen supply systems are similar to CRU systems.

Chemical oxygen generators are used on most modern aircraft.

Generators are located in service units and supply multiple masks.

Chemical reaction in generators is initiated by pulling a mask cord.

Generators release about 45% of their weight as usable oxygen.

Oxygen output from generators exceeds the amount required for emergency descent.

A relief valve prevents internal pressure from exceeding 50 psi.

Chemical oxygen generators must be treated with caution due to heat generation.

A heat-sensitive indicator shows when a generator needs replacement.

Transcripts

in this lesson we will examine the

simplemente oxygen systems provided for

passengers in cabin crew the regulations

governing the use of supplemental oxygen

throughout the aeroplane are covered in

the flight deck supplemental oxygen

lesson the supply of supplemental oxygen

to the passengers and cabin attendants

is of the continuous flow type that is

to say that once the flow to a mask is

initiated it will continue whether

someone is breathing the oxygen or not

on some smaller aircraft the flight deck

also has a continuous flow type of

system the cabin crew and passengers can

be supplied by either a high pressure

gaseous system or a chemical generator

system

the oxygen masks for the cabin crew and

passengers are stowed in the passenger

service units above the passengers heads

this picture is looking down on the top

of a typical passenger service unit the

doors of the units are opened

automatically by a barometric Li

controlled release mechanism if the

cabin altitude reaches 14,000 feet or by

manual selection by the flight crew at

any altitude there are two methods of

automatic door actuation in use in the

gaseous system they are opened

pneumatically by the oxygen pressure but

if the system uses chemical generators

the doors are opened by electrical

solenoids when the passenger service

unit doors open the masks dropped to the

half hung position that is to say they

are now hanging by their initiation

cords pulling the mask towards the face

pulls the cord which initiates the

oxygen flow by opening a check valve in

the gas supply system or operating the

electrical or percussion cap firing

mechanism on the chemical generator the

regulations require that for aeroplanes

intended to be operated above 25,000

feet the number of masks must exceed the

number of cabin seats available by 10%

with the extra masks spread evenly

throughout the cabin this allows

passengers and cabin crew not in their

seating positions to quickly find a

spare mask in the picture shown there

are only three seats below the passenger

service unit but there are four masks

stowed in the unit the oxygen enters the

mask through a plastic rebreather bag

where it is mixed with exhaled air and

cabin air

because of this mixing with cabin air

passenger oxygen masks don't give

protection from noxious fumes

a passenger high-pressure gaseous oxygen

supply system is very similar in design

to the CRU system except that the demand

regulators are replaced by mass

connection points with valves operated

by the mass cords there is also a flow

control valve in the system which can be

opened automatically by a barometric

switch when the cabin altitude exceeds

14,000 feet or manually by operation of

a flight deck switch

chemical oxygen generators which are

used on most modern aircraft are

relatively light and inexpensive

self-contained devices which require

virtually no maintenance in a system

using chemical oxygen generation the

generators are located in each passenger

cabin crew and lavatory service unit

each generator can supply to three or

four passenger oxygen masks here is a

cross-section of a typical aviation

chemical oxygen generator inside a

cylindrical case is a charge block made

up of a mixture of sodium chlorate and

iron powder this is surrounded by a

filter material and thermal insulation

in the older chemical oxygen generator

units as the mask is pulled down a cord

attached to the mask

operates a percussion cap in the firing

mechanism igniting the charge block in

more modern systems when the mask is

pulled down the cord operates an

electrical switch which fires a twenty

eight volt DC squib to begin the

ignition process when ignited the charge

brach will burn at a temperature of

approximately 200 degrees Celsius and

will burn for a minimum of 15 minutes

releasing about 45% of its weight as

usable oxygen through the oxygen outlets

the sodium chlorate and iron core is

shaped to provide maximum oxygen flow

initially this will be when the cabin

altitude is highest and the maximum

oxygen is required this table shows the

relationship between the amount of

passenger oxygen required in an

emergency descent

compared to the capacity of a typical

oxygen generator you can see that the

oxygen output is always slightly greater

than the amount required a filter in the

generator removes any contaminates and

caused the oxygen to a temperature not

exceeding 10 degrees Celsius above cabin

ambient temperature a relief valve

prevents the internal pressure in the

generator exceeding 50 psi the normal

flow pressure is 10 psi chemical oxygen

generators need to be treated with

caution the chemical reaction generates

a lot of heat the case of the generator

becomes very hot once the chemical

reaction has started it cannot be

stopped a strip of heat sensitive tape

or paint on the case changes color in

this case from orange to black when the

generator is used and provides a visual

indication that the generator needs to

be replaced

that is the end of the lesson here is a

summary of the main points

cabin crew and passenger supplemental

oxygen systems can be gaseous or they

may use chemical oxygen generators

chemical oxygen generators are usually

used because they are inexpensive light

and are almost maintenance-free in the

event of a depressurization when the

cabin altitude exceeds 14,000 feet

oxygen masks will automatically be

presented to the cabin crew and

passengers the passenger oxygen masks

can be deployed at any time by operation

of a switch on the flight deck the flow

of oxygen to a mask is normally

initiated by pulling the mask towards

the face a mixture of oxygen and cabin

air is breathed in through a passenger

mask