Below I have attached a document that I put together to try to help determine objectively what supply line should be carried and used by the AFD in the future. This is what I could put together quickly, please review it if you would and reply with any comments and/or corrections that you might have. I am looking for opinions and suggestions that will help with the process. As always 50 minds should be better than 1 looking at this. And I do have to thank Lt. Hinshilwood and FF/DO Walsh for the assistance and comments.
Please review and send me any comments by Tues. February 2nd.
Thanks.
Antarctic Fire Department Supply Line Survey
January 29, 2010
The selected maximum supply hose line length for these calculations is 1400’. This was selected based upon the distance from hydrant #4 at MMI to building 191 the Carpentry Shop. There are buildings in McMurdo that are further from a hydrant, but this is the furthest regularly occupied building from a water supply.
The calculations are based on available water flow from the hydrant. The ISO method shows a required fire flow of 2850 gpm for total involvement. So obviously the available water flow from the water system is the limiting factor. The latest hydrant flow data from hydrant #4 is 600 gpm. This data is from March of 2008 and the test was conducted with no additional pumping assistance from the water plant. Therefore, we could get 600+ gpm from this hydrant; the actual flow will require further testing.
With our current fleet in full operating condition we can support this operation at 600 gpm. It would require a dual 3” hose lay and an intermediate engine to relay pump to achieve this goal. Thing go down hill quickly at flows past 600 gpm.
Now jumping to a single lay 4” LDH we can expect some different results. At the 600 gpm flow rate, a single 1400’ line will be more than adequate. The limit for and 4” or 5” supply hose is 165 psi FL due to the maximum allowable pressure of an LDH of 185 psi and the required residual intake pressure of 20 psi. Using these numbers, you can see that the 4” hose begins to limit hose lengths at higher flows. At 800 gpm the maximum allowable length is 1300 feet. And at 1000 gpm the maximum allowable length is 900 feet.
And next with 5” single lay LDH we can expect even more distance and/or water flow. At flows up to 1000 gpm a 1400 foot line can be supported without any additional supply engines.
The other factor that I did not include in these calculations is elevation gain from hydrant #4 to building 191. The gain is approximately 80 feet, which equates to 40 psi of additional friction loss. This makes the 4” line a little sketchier in this example.As I see it for the AFD there are several pros and cons for each type of supply line.
Pros:
Dual 3” – can be used with all existing adapters, hydrants, and hose.
– total weight of 50’ roll is 38 pounds.
LDH 4 or 5” – more water flow and/or longer lays with less apparatus.
– sexless coupling require no double male/female adapters.
Cons:
Dual 3” – high friction loss and limited flow/lengths.
– dual lays require additional coordination and setup.
LDH 4 or 5” – added expense of additional adapters and couplings.
– total weight of 100’ of 4” is 68 pounds and 5” is 84 pounds.
R.J. Bragg
Captain
Antarctic Fire Department
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