Multiplace Delivery System
Monthly Hyperbaric Safety Notice: May 2006
Prevention of Future Fires in Oxygen Eduction System
In this notice, the importance of removing oxygen safely from the building housing a multiplace chamber system is discussed.
Background
The three (3) patient treatment chambers at Duke University have the capability to treat 14 patients at a time. The maximum oxygen flow through the oxygen eduction system is approximately 90 scfm. This oxygen must be removed from the building to prevent a fire hazard, but if removed with the wrong equipment, could increase risk of fire.
The Safety Issue
Historically a squirrel cage blower fan powered by an electric motor rated to move 270 scfm was used in the system to mix air with the oxygen and blow it outside the building. The system worked well for years until there was a power cord failure and a small fire had to be extinguished with a portable hand held fire extinguisher.
To eliminate the possibility of an electrical fire in the future, electrical fans exposed to high oxygen fractions, such as in oxygen eduction systems, should be eliminated. One way to remove gas with high oxygen fraction without use of electrical fans is to use air amplifiers (via use of compressed air). Air Amplifiers utilize the coanda effect, a basic principle of fluidics, to create air motion in their surroundings. Using a small amount of compressed air as their power source, Air Amplifiers pull in large volumes of surrounding air to produce high volume, high velocity outlet flows. Quiet, efficient Air Amplifiers will create output flows up to 25 times their consumption rate. Air Amplifiers have no moving parts, assuring maintenance-free operation. No electricity is required. Flow, vacuum and velocity are easy to control. Outlet flows are easily increased by opening the air gap. Supply air pressure can be regulated to decrease outlet flow. Both the vacuum and discharge ends of the Air Amplifier can be ducted, making them ideal for drawing fresh air from another location. An Exair Model 120222 Super Air Amplifier was purchased and installed with suction at the distal end of a 2” oxygen eduction manifold common to all chambers and its outlet connected to the 4 sq.ft. duct work near its exit from the building. The overboard dump system from each chamber is connected via 1” pipe to the 2” manifold, which is open at its two most proximal points. The Air Amplifier must provide enough suction to draw the oxygen output from all of the overboard dump systems and entrain air through the proximal openings of the manifold. The maximum oxygen flow through the eduction system is 90 scfm (14 single pass units at 3ATA). At 20 psi supply pressure, the output of the air amplifier is 120 scfm, the amplification ratio is 22, the air consumption is 5.5 scfm, and therefore the draw on the eduction pipe from the chambers is 114.5 scfm. Supply pressure may be increased to 100 psi yielding 400 scfm output with 18 scfm consumption.
Key Operational Issues
- Oxygen and electricity are not good partners even outside the multiplace chambers.
Bottom line
Learn from our mistakes. If you have electric motors in close proximity to oxygen sources, replace them. Any fire can be catastrophic.
Acknowledgment
This notice was taken from an abstract written by Michael J. Natoli MS CHT, Engineering Projects Coordinator for the Duke Center for Hyperbaric Medicine and Environmental Physiology.
Disadvantage of Electric Fan |
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Electric fan after fire started at the |
Original position in oxygen eduction |
System Modifications |
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Compressed air regulator used as |
Air Amplifier position in Oxygen |
Contributing Author: P. Owen Doar III, B.S.
Owen
graduated from Baptist College at Charleston, in South Carolina, in 1969. He
then moved slightly north to North Carolina, and Duke University Medical Center.
Initially employed as a hyperbaric research technician, Owen moved up the administrative
and technical framework to his present position as a manager of F.C. Hall Laboratory,
one of the premier international hypobaric and hyperbaric facilities. Owens’s
modest printed resume belies an expertise and knowledge base second to none.
He certified as a hyperbaric technologist soon after the inception of the CHT
program, is an associate member of the Undersea and Hyperbaric Medical Society
and appears as a co-author in several publications that address physiologic responses
to hyperbaric environments.
Full Panel of Safety and Technical Correspondents
Previous Multiplace Safety Notices: