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    Default SCBA questions from a student

    Hello everyone,

    I'm an Industrial (aka Product) Design student at SJSU and am taking a look at redesigning the SCBA system for fire fighters. I have a few questions however about the current system.

    From what I've read online, the tanks range from 30-60 mins. What tank do you use at your station? I also read that the actual usability of the tank is less. What is this for you compared to the tank rating?

    I understand the majority of tanks use compressed air. However, I have also read about a gas called NITROX that has around 40% oxygen, compared to 20% in the air... virtually doubling the time.

    A final question is, would it be of any use to you to have a tank that only lasted 20 mins. Basically a mini-tank. If yes, what is this situation?

    Any help is greatly appreciated. Thanks!

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    From what I've read online, the tanks range from 30-60 mins. What tank do you use at your station? I also read that the actual usability of the tank is less. What is this for you compared to the tank rating?
    We use 45 min bottles. The rating is supposed to be for an average person resting. How long the bottle actually lasts depends on exactly what activity I'm doing. In general, I expect the 45 min bottle to last about 30 mins.

    I understand the majority of tanks use compressed air. However, I have also read about a gas called NITROX that has around 40% oxygen, compared to 20% in the air... virtually doubling the time.
    I don't know of any SCBA that use NITROX. My experience with NITROX is for SCUBA diving. The increased bottom time with NITROX has more to do with the reduced nitrogen content than the air consumption rate. You still consume the air at the same rate, but the nitrogen loading in the tissue is less. This would provide no benefit that I can think of in a firefighting application and may even be dangerous due to the increased oxygen content.

    A final question is, would it be of any use to you to have a tank that only lasted 20 mins. Basically a mini-tank. If yes, what is this situation?
    I can think of no application that I would want a 20 min bottle. That would only give me about 10 min of working time.

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    Quote Originally Posted by Rogue75 View Post
    Hello everyone,

    I'm an Industrial (aka Product) Design student at SJSU and am taking a look at redesigning the SCBA system for fire fighters. I have a few questions however about the current system.

    From what I've read online, the tanks range from 30-60 mins. What tank do you use at your station? I also read that the actual usability of the tank is less. What is this for you compared to the tank rating?
    One can totally exhaust the air in the scba unit (I know, I've done it) it all depends on how hard you are breathing. My FD uses 45 minutes carbon fiber wrapped scba cylinders.

    The low air alerts are designed to sound when the air level reached 1/4 of the tank's pressure. For operations in a typical residential fire, this is adequate enough to allow the firefighter to get out for a cylinder change. In a commercial structure, where a firefighter may be 300+ feet inside in a smoke charged building, it is nowhere near enough air find the way out, especially if they are disoriented and off a lifeline or hoseline.

    I understand the majority of tanks use compressed air. However, I have also read about a gas called NITROX that has around 40% oxygen, compared to 20% in the air... virtually doubling the time.
    The air in an scba system is 78% nitrogen, 21 % oxygen, and the other 1% is everything else. The difference is it is filtered to remove any impurities.

    Nitrox is used in the scuba diving industry. It does not double the time one has using it.. it is used to increase the O2 level and reduce the need for decompression to prevent nitrogen narcosis. In the fire service, adding more O2 to the scba breathing air only adds more of an oxidizer, which supports combustion.

    A final question is, would it be of any use to you to have a tank that only lasted 20 mins. Basically a mini-tank. If yes, what is this situation?
    No.

    Years ago, Scott had what was called the "sling pak". It was designed for a fire company officer to use. Scott still makes a variation, it is for an emergency air supply for use in doing confined space operations if the air supply becomes compromised.

    In the fire service, the company officer has to stay with his crew to maintain integrity,. If the officer has to bail out after exhausting the air supply in his mini tank, where does that leave the personnel under his command? In addition, a 20 minute "minitank", on top of the scba presently used would only add to an entanglement hazard.

    Any help is greatly appreciated. Thanks!
    You're welcome!
    ‎"The education of a firefighter and the continued education of a firefighter is what makes "real" firefighters. Continuous skill development is the core of progressive firefighting. We learn by doing and doing it again and again, both on the training ground and the fireground."
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    Quote Originally Posted by Rogue75 View Post
    What tank do you use at your station? I also read that the actual usability of the tank is less. What is this for you compared to the tank rating?
    We have both 30 and 60 minute bottles. As Eng said that number is just an estimation based on the volume of air in the cylinder and the average liters/min consumed while at rest. I forget what the actual numbers are, but I believe they were posted in the forums somewhere.

    Quote Originally Posted by Rogue75 View Post
    However, I have also read about a gas called NITROX that has around 40% oxygen, compared to 20% in the air... virtually doubling the time.
    NITROX probably would not have any benefit. I forget the numbers (again) but I read somewhere that we only absorb about 20% of the oxygen we inhale. Increasing the volume of O2 in the cylinder won't increase how much your lungs can absorb. You'll just exhale more. There may be a benefit if the SCBA used some sort of rebreather that could take advantage of the remaining oxygen we exhale.

    As Eng said, NITROX is more applied to SCUBA because of the lack of Nitrogen and it's very bad side effects when at depth.

    Quote Originally Posted by Rogue75 View Post
    A final question is, would it be of any use to you to have a tank that only lasted 20 mins. Basically a mini-tank. If yes, what is this situation?
    As a primary bottle, no. Maybe as an emergency reserve but it would have to be extremely small and lightweight... Think something that would fit in my pocket.
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    Pretty much nailed everything up above. They may teach you how to manage your air with some 'skip breathing' or other techniques which can stretch the air supply beyond the rating in certain situations. I'm small, non smoker in good shape and our 30 minute bottles can last me a long time. I've had guys pinging the low air alarm and I've been sitting with 15 minutes left...everyone will use at a different rate and it's important to always pay attention to your air supply. You don't want the alarm to be the first time you are aware of how much you have left. I make it a habbit to check my supply on regular intervals and do supply checks on my crew at the same time.

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    I'll agree with everyone else in saying that I'll pass on the nitrox.

    My Department uses 30 minute carbon wrapped bottles at 4500psi. Most guys will average 15-20 minutes out of them. I would always teach my guys good air management skills, much easier now with the heads up display.

    In a residential I would go a little over 10 minutes of work time and in a commercial I will only go a little under 10 to give the increased exit/safety time to get back out of a bigger structure.

    I'd love a 45 minute bottle that was the same size/weight of the 30 minutes bottles. I use the little mini bottles on occasion when I'm teaching, sometimes its easier to take in the little "short-snort" bottle and be able to talk to the kids and move fast rather than wear the big tank and talk through the voice amp.

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    Quote Originally Posted by Rogue75 View Post
    I understand the majority of tanks use compressed air. However, I have also read about a gas called NITROX that has around 40% oxygen, compared to 20% in the air... virtually doubling the time.
    In addition to what the others have said about the NITROX (mainly for scuba diving, no real advantage in firefighting,etc.) there is also the issue of cost. Filling SCBA cylinders with NITROX would be more expensive than filling a cylinder with plain air. If you're a busy city department filling dozens (maybe hundreds, I don't know) of cylinders a day, or a volunteer department without a lot of cash, filling with NITROX could get expensive.

    Air is free

    A final question is, would it be of any use to you to have a tank that only lasted 20 mins. Basically a mini-tank. If yes, what is this situation?
    When you get to working in one, a 30 minute cylinder will only last about 20 minutes (or less). You really wouldn't want to go into a situation with less than that. As Gonzo mentioned, the small 5-minute escape cylinders are sometimes used in confined space entry, where the entrants will be working on an air line supplied from a cylinder bank outside the confined space. This supply is only designed to allow the worker to escape from the space in the event his air supply is compromised. They are a common item in the plant where I work, where we do a lot of confined space entries.
    Last edited by dmleblanc; 10-22-2009 at 11:33 AM.
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    Good luck on reinventing the wheel.
    Stay Safe and Well Out There....

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    Quote Originally Posted by shenry32 View Post
    much easier now with the heads up display.
    HUD! We just got running water and electricity 5 years ago and you have HUD!! j/k...I guess I didn't realize you could get such a thing. Man we need new packs.

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    As several have said here, there are smaller cylinders available. Ranging in size from 5 minute to 15 min, I use a lot of them in the oil industry, primarily dealing with toxic gas, namely H2S. They are supplied air, in the event of an emergency, you unplug airline, turn on cylinder and get out of Dodge. I don't really envisage much use in the fire service.

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    Thank you all gentlemen!
    You have all been quite informative & valuable to my project research.

    Thanks again!

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    Rogue,

    Is that San Jose State University? If it is I have a friend from high school many years ago who is a Doctoral Fellow in the Engineering College.

    If you are in the Graduate level design courses you may have him. What is the course ID?

    Anyways.....

    We use 45 minute cylinders.

    As I think it was stated the cylinders are not he issue, the packs and level indicator systems are the areas for improvement. It would be great to come up with a pack that did not use batteries.

    Also forums members, as I am typing this I think I recall this same type of question several years ago and it ended up being a sales push. I think I will do some searching.

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    "45 min" tanks.

    No on the Nitrox. If needed, you can usually refill a tank from apparatus on scene. Nitrox would just be another system to deal with and having to train more people.

    I don't think a shorter time bottle would do any good except for a RIT to get someone out, but that's more to carry since you can usually fill off your own tank.

    Now if you could come up with a smaller tank that offers the same potential time, that might be something that would get interest.

    Good luck!

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    We use 30 minute 2216 bottles.

    As for nitrox - forget it. Now trimix, that might have some actual benefits (not likely worth the cost though). Trimix basically adds helium to the mix. This does 2 things, first it can reduce the gas weigh you are carrying. That likely wouldn't be seen as much on the 30 minute bottles but its could be noticeable in the 60 minute bottles. The other factor is density. Helium/trimix has a much lower work of breathing than good ol air due to the differences in dentity. Its noticiable when diving but then again, at 200' where I last used trimix, the air is 7 times denser than at the surface so any little bit helps.

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    Lightbulb

    I think that if you incorporated the smaller "rescue" tank into the SCBA system that would be a good start. Right now you have the bottle on your back and that's it. But say you built a spare bottle with approx. 20 min. of air in it that was stored inline next to the main bottle that would be great. Make it so that if you fully exhaust your main bottle, it kicks over to the escape bottle. Does that make sense to everyone? As anyone who has sucked a mask onto their face, there is a great vacuum that is created. Use that vacuum to "switch" the bottle. No flicking a switch, nothing to get hung up on. It could be stored right behind and above the pass alarm sensor on your hip going horizontally. Of course the low air alarm would continue to sound but it could mean getting you those few extra steps to get out the door or window.

    Just my idea. I hope you like it and incorporate it into your plans.
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