9.1 Portable Oxygen Cylinders & Protective Breathing Equipment

Portable Oxygen Cylinders & Protective Breathing Equipment

During flight operations, cabin crew members must be fully prepared to handle atmospheric emergencies, cabin depressurization, passenger medical distress, and in-flight fire or smoke events. The two primary life-support devices carried in the aircraft cabin to address these hazards are Portable Oxygen Cylinders (POC / POB) and Protective Breathing Equipment (PBE / Smoke Hood). Compliance with Nigerian Civil Aviation Regulations (Nig. CARs) Part 2 and ICAO Annex 6 mandates that all cabin crew maintain thorough knowledge of the location, pre-flight inspection, operating procedures, duration calculations, and safety precautions for this critical emergency gear.

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Portable Oxygen Cylinders (POC / POB)

Portable Oxygen Cylinders (commonly referred to as POBs or POCs) are high-pressure steel or composite bottles containing aviator's breathing oxygen. They provide supplemental oxygen to crew members who must move around the cabin following a sudden decompression, as well as therapeutic oxygen to passengers suffering from hypoxia, cardiac distress, dyspnea, or post-decompression trauma.

Outlet Configurations & Flow Rates

Standard commercial aircraft POBs feature dual outlets or selectable metering valves offering two distinct flow rates:

1. High Flow Outlet (4 Liters per Minute - 4 L/min):

   • Primary Indication: Used for severe hypoxia, cardiac arrest, major shock, unconscious passengers, or cabin crew members conducting post-decompression cabin surveys and physical work.
   • Oxygen Delivery: Delivers a higher concentration of oxygen to rapidly elevate arterial blood oxygen saturation (SpO2).

2. Low Flow Outlet (2 Liters per Minute - 2 L/min):

   • Primary Indication: Used for mild respiratory distress, hyperventilation, general therapeutic maintenance, or elderly/infant passengers requiring prolonged support.
   • Oxygen Delivery: Conserves bottle pressure while maintaining steady therapeutic oxygenation.

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POB Duration Calculations & Safe Cut-off Thresholds

Cabin crew members must be capable of calculating remaining oxygen duration during an in-flight medical or decompression emergency. The basic operational duration equation accounts for usable cylinder volume and flow rate:

Duration (minutes) = Usable Cylinder Volume (Liters) / Outlet Flow Rate (L/min)

However, in practical flight operations, a 200 PSI residual pressure rule must always be observed. Cylinders must never be depleted below 200 PSI (13.8 bar) to prevent ambient moisture, cabin humidity, and atmospheric contaminants from entering the valve assembly and causing internal cylinder corrosion.

Worked Example: Cabin Oxygen Duration Calculation

Scenario: A passenger requires therapeutic oxygen via a 311-Liter POB. The pre-flight pressure gauge reads 1800 PSI. If the crew connects the mask to the Low Flow outlet (2 L/min), what is the maximum safe operating time before reaching the 200 PSI reserve threshold?

1. Calculate Usable Pressure Ratio: Usable Ratio = (Current PSI - Reserve PSI) / Full Capacity PSI = (1800 - 200) / 1800 = 1600 / 1800 = 0.889

2. Calculate Total Theoretical Duration at Low Flow (2 L/min): Total Theoretical Duration = 311 L / 2 L/min = 155.5 minutes

3. Calculate Safe Available Duration: Safe Duration = 155.5 x 0.889 = 138.2 minutes

Result: The cabin crew can safely administer oxygen for approximately 138 minutes before the pressure drops to the 200 PSI cutoff mark.

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POB Pre-Flight Inspection Criteria

Before every flight departure, cabin crew assigned to equipment checks must physically verify each POB against the following regulatory criteria:

• Pressure Gauge Reading: Must register between 1500 PSI and 1800 PSI (full charge). Any bottle reading below 1500 PSI must be reported to the Lead Cabin Crew / Purser and flight deck for replacement under the Minimum Equipment List (MEL).
• Mask Assembly: At least one constant-flow rebreather mask must be securely plugged into the High Flow outlet (or designated outlet per airline SOP), with tubing free of kinks.
• Spare Mask: A secondary mask sealed in an airtight plastic bag must be attached to the cylinder body via a strap.
• Carrying Strap: Canvas or nylon shoulder harness must be intact, undamaged, and correctly clipped to the cylinder.
• Physical Condition: Cylinder body free of deep scratches, dents, or chemical contamination. Gauge glass must be clean and uncracked.
• Cleanliness: Zero presence of oil, grease, or cosmetic petroleum products on or near the valve assembly.

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Therapeutic vs. First Aid Oxygen & Critical Safety Rules

• Therapeutic Oxygen: Administered to passengers suffering from non-emergency chronic conditions or mild in-flight illness under standard cabin pressure.
• First Aid / Post-Decompression Oxygen: Administered immediately after a cabin decompression once the aircraft has descended to a safe altitude (10,000 feet MSL or below). Crew members use POBs to maintain physical mobility while attending to injured passengers or checking lavatories.

Crucial Safety Precautions:

1. Prohibition of Petroleum Products: Pure high-pressure oxygen violently accelerates oxidation. Contact between pure oxygen and petroleum-based products (such as lip balm, vaseline, makeup, oil, or grease) can cause instant spontaneous combustion and explosion. Crew members and passengers must wipe off all lip balm before donning an oxygen mask.
2. Stowage During Administration: During use, the POB must be secured in an adjacent seat, held securely by a crew member using the shoulder strap, or strapped under a seat to prevent it from becoming a heavy projectile during turbulence.
3. Ignition Source Distance: Keep operating POBs at least 10 feet (3 meters) away from open flames, electrical sparks, galley ovens, or discharged fire extinguishers.

Protective Breathing Equipment (PBE / Smoke Hood)

Protective Breathing Equipment (PBE), universally known as the smoke hood, is a self-contained, portable respiratory protection device designed to protect cabin crew members from toxic gases, dense smoke, and oxygen deficiency while fighting in-flight fires or performing cabin evacuations.

+-------------------------------------------------------------------------+
|                    PROTECTIVE BREATHING EQUIPMENT (PBE)                 |
|                                                                         |
|  +-------------------+  +---------------------+  +-------------------+  |
|  | Outer Container   |  | Inner Vacuum Pouch  |  | Chemical O2       |  |
|  | - Hard Case Box   |  | - Foil Enclosure    |  |   Generator       |  |
|  | - Tamper Seals    |  | - Tear Notches      |  | - KO2 / NaClO3    |  |
|  | - Inspection Window| | - Humidity Indicator|  | - Starter Ring    |  |
|  +-------------------+  +---------------------+  +-------------------+  |
|                                                                         |
|  +-------------------------------------------------------------------+  |
|  | Hood Assembly: Visor, Inner Nose-Cup, Elastomeric Neck Seal        |  |
|  +-------------------------------------------------------------------+  |
+-------------------------------------------------------------------------+

Chemical Oxygen Generation vs. Compressed Gas

Modern commercial transport aircraft utilize two main types of PBE systems:

1. Chemical Oxygen Generator PBE (e.g., Dräger, Avox/SCOTT, Essex):

   • Uses a solid chemical candle containing Potassium Superoxide (KO2) or Sodium Chlorate (NaClO3).
   • Pulling the starter ring ignites an internal striker that initiates an exothermic chemical reaction.
   • As the wearer exhales, moisture and carbon dioxide (CO2) are chemically absorbed by the KO2 bed, which simultaneously releases pure oxygen back into the hood breathing circuit.

2. Compressed Gas PBE (e.g., Puritan Bennett):

   • Utilizes a small internal cylinder of compressed aviator's oxygen.
   • Pulling the activation lanyard opens a pin-valve, releasing a continuous flow of compressed gas into an inner visor mask and neck diaphragm.

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PBE Pre-Flight Inspection Checklist

Cabin crew must inspect every PBE at its designated stowage location (stowed within 3 feet / 0.9 meters of every hand-held fire extinguisher) prior to flight:

1. Stowage & Security: PBE container or bracket is firmly latched in its designated location.
2. Tamper-Evident Seals: Check that external tamper seals (yellow, red, or wire tags) on the outer container are intact and unbroken.
3. Humidity Indicator Status: Inspect the humidity indicator visible through the transparent viewing window of the inner vacuum bag:
   • Serviceable Colors: Green (Dräger PBE) or Blue (Avox / SCOTT / Essex PBE).
   • Unserviceable Colors: Pink, White, or Brown. Any pink or white coloration indicates moisture has breached the vacuum bag, rendering the chemical generator degraded and unserviceable. Report immediately for replacement.

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PBE Donning Procedure (6-Step Protocol)

In the event of a cabin fire or dense smoke, cabin crew members must don the PBE within seconds using the standardized 6-step protocol:

1. Retrieve & Open: Remove PBE container from wall bracket, break tamper seals, and open the container lid.
2. Remove Vacuum Pouch: Pull the foil vacuum pouch out of the hard case and tear it open using the designated corner tear notches.
3. Activate Oxygen Flow: Grasp the pull-ring or actuation strap firmly and pull sharply in the direction indicated by arrows to trigger the chemical starter candle or open the gas cylinder.
4. Expand Neck Seal: Insert both hands into the rubber neck seal opening with palms facing outwards and thumbs pointing inward, stretching the neck seal wide open.
5. Don Hood Over Head: Bend forward at the waist and slip the hood over the head from back to front, ensuring the rubber neck seal passes cleanly over hair and sits snugly around the neck without catching shirt collars or hair.
6. Adjust Nose-Cup & Verify: Pull the inner oral-nasal cup over the nose and mouth, verify clear vision through the anti-fog visor, and confirm the sound of oxygen flow.

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Operating Specifications & Post-Use Handling

• Operating Duration: Provides a minimum of 15 minutes of continuous breathable oxygen under active firefighting workload conditions.
• Operational Indicators: Active flow of oxygen, inflation of the inner hood membrane, and clear visor. Near the end of its 15-minute life, the hood will begin to deflate slowly, and oxygen flow noise will diminish.
• Post-Use Removal & Disposal:
  • Remove the PBE by expanding the neck seal and pulling the hood off from front to back, away from hot surfaces.
  • WARNING - Hot Chemical Canister: The chemical generator canister located at the back of the hood reaches temperatures exceeding 80 degrees C (176 degrees F) during operation. Do NOT touch the canister body directly.
  • Place spent PBE in a designated safe, non-flammable area (e.g., metal galley container or lavatory floor) to cool.
  • After removing PBE, crew members must vigorously brush their hair with their hands to dissipate any pure oxygen trapped in their hair before approaching open flames or ignition sources.