Editor's note: Many readers responded to our article on Bill Lambert, an engineer from Mine Safety Appliances (MSA) who leads a team developing the breathing apparatus and other equipment that protects firefighters. The original article, Lifer in the fire wars, appeared in the 03.11.03 of Design News. Or go towww.designnews.comand key in "Lambert" in the search box.
I read your article on SCBA's (Lifer in the fire wars, DN 03.11.02). As a call Firefighter I appreciate the value of breathing air in a toxic environment. Any department that asks for new SCBA equipment and gets a bunch of questions should show this article to budget committee and local governing body.
I am glad that since 911 people are more aware of the dangers that firefighters face day by day. I would like to thank Mr, Lambert for literally getting involved with the development of SCBAs. He is indeed an ally of the Fire Service. My final wish is to send on my prayers and thoughts to the families of firefighters affected by events of 9/11, not forgetting any of the many other tragic fires that have taken lives in the fire service.
An avid SCUBA diver, I carry my tanks with the valves and regulator in the upright position, yet SCBA cylinders and regulators are mounted upside-down. I've always assumed it was because of the heat and trying to protect the regulator. Is there a technical reason for this?
George Gilligan
MSA's response: SCBA regulators are not really mounted differently from a SCUBA regulator. The first stages of SCUBA gear are generally mounted at the cylinder outlet and the second stages are mounted close to the user's mouth. SCBA first-stage regulators are mounted either at the cylinder outlet (which as discussed below is located at the bottom of the cylinder) or on the backframe (which is where ours happens to be). There is no overriding reason for this, just manufacturer/user preference or opinion. Like SCUBA, SCBA second-stage regulators are generally located at the mouth. The cylinders are another story. SCBA are usually worn with a fire helmet that has a large brim in the back and therefore clearance at the top of the cylinder in the back is critical. Mounting the cylinder valve down eliminates this problem.
Reader Allen Wollscheidt (Sun Lakes, AZ) had the following questions:
Q: What gas is stored in the SCBA tanks?
MSA: SCBA tanks hold compressed air, at pressures up to 4500 psig.
Q: Any consideration given to recycling/cleaning air supplies rather than throwing them away?
MSA: I'm not sure I understand the question. The compressed air in the cylinder can be replenished many times. The cylinders have a life of 15 years to infinite, providing that they pass periodic (frequency depends on construction of pressure vessel) inspection and testing. These requirements are governed by the U.S. Dept. of Transportation.
Q: Could a firefighter wear two or three tanks?
MSA: Many people may think that the physical burden appears minimal, and that the Quick Flow valve system would make it easy to carry and use several tanks. There are SCBA configurations with multiple tanks. These are most commonly used in Europe. The problem with multiple tanks is that the total weight is greater for a given stored volume as compared to a single larger cylinder (remember that SCBA are not used under water where buoyancy assists in carrying the load). The profile (distance from the wearer's back) is smaller for multiple cylinders, so there are tradeoffs.
Q: Does the flow rate adjust to an analyzed respiratory need?
MSA: Today's SCBA are pressure-demand type devices, which means that the flow from the regulator tracks the demand, always maintaining a slight positive pressure in the facemask. If the user is not inhaling, the regulator does not flow.
As a volunteer firefighter and engineering professional, I readily appreciate MSA's and Bill Lambert's efforts to improve SCBA's.
Ergonomics is a major firefighter consideration. NFPA structural gloves are thick and bulky. Operating PASS devices, knobs, straps, couplers and bypass valves on SCBA units is made difficult because sizes and shapes are suboptimal in a fire, where glove removal could be deadly. Bright/luminous materials could improve visual recognition. Faceshields fog up and smoke particles attach to the exterior, reducing visibility. Cleaning, drying, and storing for reuse can also be tedious.
SCBA units often donned from seat mount brackets which can be tricky to use as well. Nylon webbing is strong but straps/buckles are too easily tangled. Semi-rigid belt guides and an integrated approach to overall pack design could provide significant gains in speed and safety. A look back at early SCUBA designs exhibits iterative development into today's unitized pack.
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