Oxygen Supply Systems: Cylinders, Liquid, and Concentrators

Oxygen Supply Systems: Cylinders, Liquid, and Concentrators

Oxygen is the most commonly used medical gas in respiratory therapy. Understanding how oxygen is stored, delivered, and calculated is a core clinical skill — and a patient safety responsibility. This lesson covers three supply systems: compressed gas cylinders, liquid oxygen systems, and oxygen concentrators.

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Compressed Gas Cylinders

Medical oxygen is stored in steel or aluminum cylinders under high pressure. Cylinders are color-coded green in the US (or have a green label) and must be clearly labeled "Medical Oxygen" and meet Department of Transportation (DOT) specifications. Never assume a cylinder's contents from color alone — always read the label.

Common sizes:

• E-cylinder — portable size, commonly used at the bedside and for patient transport. Holds approximately 625 liters when full (at roughly 2,000 psi).
• H-cylinder — large bulk cylinder used in hospital central supply or home settings. Holds approximately 6,900 liters when full.

Key components:

• Valve — the on/off control at the cylinder neck. Open slowly; never force.
• Regulator — reduces high tank pressure to a safe working pressure.
• Flowmeter — controls and displays the flow rate in liters per minute (L/min).
• Bourdon gauge — a pressure gauge that displays the remaining pressure in pounds per square inch (psi). This reading is used in duration-of-flow calculations.
• Cylinder wrench — required to open valves on some cylinders (E-cylinders especially). Keep the wrench attached to the cylinder during use.

Safe handling steps:

1. Secure the cylinder — always chain or strap cylinders upright to a wall bracket or transport cart. A falling cylinder can become a dangerous projectile.

2. Crack before attach — briefly open the valve one-quarter turn and close it immediately to blow out dust before attaching the regulator. Point the valve away from people.

3. No oil, no grease — oxygen under pressure can react violently with petroleum-based lubricants. Never use oil or grease on valves, regulators, or connections.

4. Turn valve off when not in use — prevents slow leakage and reduces fire risk.

5. Store away from heat and ignition sources — NFPA 99 (Health Care Facilities Code) governs cylinder storage areas in health care settings, including quantity limits, ventilation, and segregation of full versus empty cylinders. Always follow your facility's NFPA 99-based policy.

6. Mark empty cylinders — label empties clearly and store them separately from full cylinders to prevent accidental use.

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Cylinder Duration-of-Flow Formula

Knowing how long a cylinder will last at a given flow rate is critical for patient transport and home care planning.

Formula:

> Duration (minutes) = (Cylinder pressure in psi × Cylinder factor) ÷ Flow rate (L/min)

Cylinder factors (established constants based on cylinder volume):

• E-cylinder: 0.28
• H-cylinder: 3.14
• D-cylinder: 0.16
• G-cylinder: 2.41

These factors account for the cylinder's internal volume. Memorize the E and H factors — they appear in clinical practice and on credentialing exams.

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Liquid Oxygen Systems

Liquid oxygen (LOX) is oxygen cooled to an extremely low temperature (~−183 °C / −297 °F), which allows a large volume of gas to be stored in a relatively small, lightweight container.

System components:

• Stationary reservoir — a large, insulated base unit kept in the home or facility.
• Portable unit — a smaller, lightweight vessel the patient fills from the stationary unit and carries when leaving home.

Clinical and safety considerations:

• LOX produces a large volume of gas when it warms to room temperature — spills can cause rapid oxygen enrichment of the surrounding air, dramatically increasing fire risk.
• Contact with liquid oxygen causes severe frostbite. Use insulated gloves when transferring liquid.
• Portable units vent continuously as oxygen evaporates ("boil-off"). Store in ventilated areas; never store a venting LOX unit in a closed vehicle or closet.
• Check the weight gauge or contents indicator regularly; liquid systems do not use psi gauges like compressed gas cylinders.
• LOX systems are preferred for ambulatory patients who need high flow rates, because they provide more oxygen per unit weight than cylinders.

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Oxygen Concentrators

An oxygen concentrator is an electrically powered device that separates oxygen from room air using a molecular sieve (zeolite) material. It does not store oxygen — it produces oxygen continuously from ambient air.

Key features:

• Delivers oxygen at concentrations typically 90–96% at lower flow rates; purity decreases as flow rate increases.
• A purity indicator or alarm alerts the user if oxygen concentration drops below an acceptable threshold (commonly below 85–90%, depending on device).
• Standard home units deliver up to 5–6 L/min; high-flow models may deliver more.
• No cylinder refills needed — suitable for long-term home oxygen therapy.
• Backup cylinder required — power outages stop oxygen production; patients must have an emergency cylinder available.
• Requires regular filter cleaning and maintenance per manufacturer schedule.
• Not suitable for use near open flames; the enriched oxygen environment supports combustion.

Alarms to recognize: Low purity alarm, power failure alarm, high-temperature alarm. Investigate any alarm before assuming it is a false alert.

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General Oxygen Safety Principles

Oxygen does not burn, but it vigorously supports combustion. These rules apply to all oxygen delivery systems:

• No smoking within an established safe radius of any oxygen in use.
• No open flames, candles, or gas appliances near oxygen equipment.
• Keep oxygen equipment away from electrical sparks.
• Educate patients and caregivers on every safety point before discharge with home oxygen.

Following OSHA workplace safety standards and NFPA 99 guidelines protects both the patient and the respiratory therapist. Scope-of-practice adherence and thorough documentation are professional and legal obligations tied directly to your State RT License.