Oxygen Tank Pressure

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

Oxygen Tank Pressure

For many reasons, patients that require additional oxygen use storage tanks with compressed oxygen to supplement their normal air intake.  The size and subsequent capacity of the tank may vary but the full pressure is typically about 2,000 psi and can go as high as 3,000 psi. With this pressure level in the tank, a regulator converts the supplied pressure to a lower, and much safer, level for the user. With newer aluminum and other materials instead of steel to avoid magnetism problems in situations such Magnetic resonance Imaging (MRI) tests, the pressure level is lower. Minimum pressure in tanks is around 300 psi with delivery systems operating at pressure below 400 psi. In contrast, the storage and delivery system of liquid oxygen in a hospital, pressures are usually around 50.0–55.1 psi. The amount of oxygen present inside the cylinder is measured by the pressure at the outlet nozzle.

PV/T = constant

where P is pressure in the cylinder,

V is the volume of the cylinder,

and T is the temperature

Applied Home Healthcare Equipment

Image courtesy of Applied Home Healthcare Equipment.

Normal clean air contains 19% to 21% oxygen. In contrast, a supply of 60% oxygen with 40% nitrogen is considered acceptable for most clinical purposes but usually high much higher content is available.

Portable oxygen cylinders often have flow and pressure gauges. They provide easy, on sight measurements for a user. However, remote monitoring can use microelectromechanical systems (MEMS) pressure sensors to provide an electrical signal that can be transmitted to one or more receivers.  With this information displayed remotely, a variety of healthcare givers can access and use the information.

Comments/Questions?
Do you have a pressure sensing question? Let us know and we’ll address it in an upcoming blog.
Email us at info@allsensors.com

Airplane Oxygen Pressure

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities and you. In this blog we’ll discuss airplane oxygen pressure.

Airplane Oxygen Pressure

You hear it every time you fly on a commercial airline: “If a drop in cabin pressure occurs, oxygen masks will drop down. Oxygen is flowing even though the bag does not inflate.”

oxygenmask

As a pressure sensing proponent, this raises three questions: What is the tank pressure? What is the line pressure? What pressure drop occurs in the line?

While aviation regulations require that an emergency oxygen supply is available to passengers if there is a loss of cabin pressure, storing oxygen in tanks would add weight, complexity and maintenance issues to those already required for each airplane. As a result, the majority of commercial aircraft use chemical oxygen generators to provide emergency oxygen for passenger cabin occupants. Pulling down the oxygen mask releases the firing pin and activates the generator.

With this process, the three pressure sensing questions are moot. However, there are other pressure issues involved.

According to “Chapter 16: Cabin Environmental Control Systems,” “At sea level, oxygen pressure in the lungs is approximately three pounds per square inch (psi).” Without supplemental oxygen, this level drops to 1.74 psi at 15,000 mean sea level (MSL) and oxygen transfer to the bloodstream drops to 81% of saturation, typically resulting in sleepiness, headache, blue lips and fingernails, and increased pulse and respiration.

Pressurizing the passenger compartment avoids the problem of lower oxygen transfer – until a loss in cabin pressure occurs. In addition to the chemical oxygen generators, oxygen tanks are usually used for the crew in commercial airplanes and other non-commercial airplanes. The storage tanks have different rated pressures.

Certification Type Material Rated pressure (psi)
DOT 34A Steel 1,800
DOT 3HT Steel 1,850
DOT-E-8162 Composite 1,850
DOT-SP-8162 Composite 1,850
DOT 3AL Aluminum 2,216

In the oxygen tank system, a pressure regulator lowers the oxygen pressure from the storage cylinder(s) to approximately 60 to 85 psi and delivers it to individual regulators dedicated for each user where further pressure reduction occurs.

So sit back and relax. There are many reasons why flying is among the safest ways to travel.

What do you think/Comments?
Do you have a pressure sensing question? Let me know and I’ll address it in an upcoming blog.
-Han Mai, Marketing Coordinator, All Sensors Corporation (hmai@allsensors.com)