To my knowledge, there has never been a safety factor requirement in NFPA 13 or any of the National/International Codes. Typically, when required it is a jurisdictional, insurance or project specification requirement.
Like Travis said, the safety factor isn't regulated by NFPA or IFC. In my dealings, most jurisdictions have required a 10% safety factor for sprinkler design. Contact the AHJ of your project and ask what their requirements are.
Yea BUT from NFPA 13 2007 ED, also in 2010 ed of 13
23.2.1.2 The volume and pressure of a public water supply
shall be determined from waterflow test data. An adjustment
to the waterflow test data to account for daily and seasonal
fluctuations, possible interruption by flood or ice conditions,
large simultaneous industrial use, future demand on the water
supply system, or any other condition that could affect the
water supply shall be made as appropriate.
A.23.2.1 Care should be taken in making water tests to be
used in designing or evaluating the capability of sprinkler systems.
The water supply tested should be representative of the
supply that might be available at the time of a fire. For ex-ample, testing of public water supplies should be done at times
of normal demand on the system. Public water supplies are
likely to fluctuate widely from season to season and even
within a 24-hour period. Allowance should be made for seasonal
or daily fluctuations, for drought conditions, for possibility
of interruption by flood, or for ice conditions in winter.
Testing of water supplies also normally used for industrial use
should be done while water is being drawn for industrial use.
The range of industrial-use demand should be taken into
account. In special situations where the domestic water demand
could significantly reduce the sprinkler water supply,
an increase in the size of the pipe supplying both the domestic
and sprinkler water can be justified.
Future changes in water supplies should be considered. For
example, a large, established, urban supply is not likely to
change greatly within a few years. However, the supply in a
growing suburban industrial park might deteriorate quite rapidly
as greater numbers of plants draw more water.
This is what be reference when we ask for 10 psi OR 10% what ever is higher.
****************************************
Fire Sprinklers Save Firefighters’ Lives Too!
So how many water flow tests meet the above requirements?
THEN we use a computer to design a sprinkler system with a demand of 459 gpm @56.34 psi and available 56 psi @ 459 gpm. AND folks want to know why I rejected the plans?
How many have used a pitot to conduct the hydrant flow test and looked at the gauge and picked a number because it was bouncing from 60-66 psi??
Really?? a .34 psi safety cushion???
****************************************
Fire Sprinklers Save Firefighters’ Lives Too!
There is inherent safety factor in almost all systems. This shows up in the very high % of success in properly designed and maintained systems. I have seen numbers from New Zealand I think it was of 99%+ success (not counting where somebody goofed).
I cant enforce some arbitrary margin and you can bet the contractors don't do it on their own.. . We require 3,000 sq ft design area (or less QR reduction). That is ALL the safety margin. I've had to accept plans where water supply and demand were within 0.01 psig and for 98 psig residual... Smelled really fishy but if I fight and lose the bill from the contractor can come out of MY PAYCHECK. It's called unauthorized obligation on behalf of the government, and if the contractor complains he is always always right. Career government contractors know this and they do terrible work but once they are in you can't get rid of them.. The appeals boards are a bunch of wimps who can be pushed over in a slight breeze. It's like they don't even listen to the govt employees and just assume the contractor is entitled and we govt employees are just trying the create waves.. I came near to losing a battle where the contractor didn't sprinkle a combustible overhang and change ordered us $60k to add 4 more heads off the dry system.. Like NFPA 13 requires. Should have been a slam dunk but I was really sweating it and thinking there goes my 401k.
So yeah no enforcement of safety margin here.. I wonder how anyone else can legally enforce it. I guess failing the plans and withholding the CofO works but it seems like there might be lawsuits there also..
Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.
Many jurisdictions have it written in their adopted local codes. That is how it is enforced. The other way to get one is to require the contractor to prove they have the seasonally adjusted peak demand time for their water flow test. Lastly, if there is 0.01 psi safety margin, have the contractor provide calculated as-builts to verify that the project went in exactly per plans.
See Above NFPA 13 code section 1323.2.1.2. That is HOW you enforce it.
So where in NFPA 13 does it say you need 3000 sq. ft?? If you require such a large design area then why not a safety cushion?? Just do not understand your logic.
****************************************
Fire Sprinklers Save Firefighters’ Lives Too!
Georgia requires a minimum 10 psi safety factor in all jurisdictions.
In addition new rules going into effect the first of the year require a 24 hour pressure test with the design to the lowest pressure available in a one hour span.
If your test indicates 60 static, 50 residual @ 1,000 and the 24 hour test indicates a one hour period where the static pressure dropped to 50 psi then your design would be to 50 static, 40 residual @ 1,000 with the required 10 psi safety factor.
All tests must be conducted in the previous six months.
Tests must be done with calibrated test gauges and you better be prepared to send the gauge documentation in with your submittals.
Recently I've gone so far as to take video of my flow tests parking the video in my file in case anyone ever wants to see it.
It is very good in Georgia I love working here. Everyone knows the rules, they are all published, and it's a level playing field.
Another thing about Georgia is like many states budgets are being cut and the state fire marshals office is no exception. To counter this the new rules are making those of us who hold the certificates for the company more responsible for self policing. I must personally visit all jobs a minimum of three times, each of these visits are documented and sign by the owner/general contractor and I must be there to sign off 1)rough in, 2)80% completion, 3) 100% completion and to witness the hydrostatic test. The days of some fitter signing off the hydro are over.
Then the certificate holder for the company signs a completion certificate saying he's inspected the entire job and how it meets all code requirements. All this paperwork is sent to the state for safe keeping.
If something is found wrong in the future they know exactly whose license to go after and I have been warned that is the whole purpose. I am a whole lot more careful today than I was three years ago and I will be more careful in the future starting now.
Someone that is slothful has a target on their back.
I wish I had language like Georgia to rely on. I completely understand all points made above, and believe me I have tried them, but what i am saying is that at the end of the day, unless a local code says 10 psig, you can not force a margin of safety, even if that is the intent of the standard. The designer is free to do as they see fit, and forcing it is legally risky.
I take some consolation and rationalize this away by knowing that in almost all cases 4 heads (<900 sq ft) will do the job.. Assuming the system is properly maintained and hazards don't increase. So a water supply good for more than that area can probably handle the fire even if the water supply fluctuates.
Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.
(18) NFPA 20, 2003 Edition, Standard for the Installation of Stationary Pumps for Fire Protection
Modifications:
(a) Modification to Chapter 2:
1. Add a new paragraph 2-1.1.1 to read as follows:
“2-1.1.1 At 150% rated capacity or below, the pump suction supply shall not drop below 20 psi (1.38 bar).
Exception: Suction supply pressure may be lowered upon approval of the authority having jurisdiction.”
9.4.3 BOOSTER PUMPS - Booster pumps shall be located or controlled so that:
a. they will not produce negative pressure anywhere in the distribution system. b. the pressure in the suction line shall be maintained at or above 20 psi by the use of a pressure sustaining valve or low pressure cutoff device.
c. automatic or remote control devices shall have a range between the start and cutoff pressure which will prevent excessive cycling.
9.4.4 IN-LINE BOOSTER PUMPS - In addition to the other requirements of this section, in-line booster pumps shall be accessible for servicing and repairs. 9.4.5 FIRE PUMPS - The criteria in this section also apply to fire pumps.
again on page 31 has to do with standpipes in buildings other than high rise (Exception 3):
2. Delete 7.8.2.1 in its entirety and substitute in its place the following:
“7.8.2.1 Pipe schedule designed standpipe systems shall have piping sized in accordance with the pipe schedule in Table 7.8.2.1 to provide the required waterflow rate at a minimum residual pressure of 100 psi (6.9 bar) at the topmost 2-1/2 inch (65 mm) hose connection and 65 psi (4.5 bar) at the topmost 1-1/2 inch (38 mm) hose connection.
Exception No. 1: Where the local Fire Chief or local Fire Code Official having fire suppression jurisdiction permits lower than 100 psi (6.9 bar) for 2-1/2 inch (65 mm) hose connections, based upon local suppression tactics, the pressure shall be permitted to be reduced to not less than 65 psi (4.5 bar). Exception No. 2: Where the building is protected throughout by a supervised automatic sprinkler system and the building is not a high-rise, as defined in 3.3.9, the minimum residual pressure provisions shall not be mandatory when the standpipe system piping is a minimum of eight inches (8”) nominal diameter.
Exception No. 3: Existing high-rise buildings, as defined in 3.3.9, that are protected throughout by a supervised automatic sprinkler system shall be permitted a reduction of the minimum residual pressure requirement of 100 psi (6.9 bar) at the hydraulically most remote 2-1/2 inch (63.5 mm) hose connection to 65 psi (4.5 bar).”
I've used it, install all 8" pipe on a five story motel (as long as it doesn't exceed 75' to the top floor) and not have to have a fire pump. This is especially important when in a city like Savannah where all pumps must be diesel or have a transfer switch.
Manual standpipes are not allowed in Georgia with the exception of open parking garages.
Everyone in Georgia must follow the state minimum standards unless the local authority wants to be more stringent. Even here the local authority isn't a dictator, for example Dalton, Georgia requires sprinklers in all attics of NFPA 13R systems but to be able to enforce it they had to do two things; 1)Have legislation passed by the local city building department and 2)submit that legislation to the state fire marshal's office for approval who publishes the requirement upon approval. This keeps everyone on an even playing field.
I had a 13R job where the local authority insisted upon sprinklers in the attic. I told him no, it wasn't required and was told my plans would be rejected. I contacted the state fire marshal who stepped in telling the local authority they couldn't require sprinklers in the attic so I didn't.
I have worked and been licensed in Alabama, Florida, Georgia, Nebraska, Ohio, South Carolina and Kentucky. In my never humble opinion Georgia has the best setup followed closely by Kentucky. I love it here, the line is clearly visible in the sand, it's published and fairly applied to all.
Licensing requirements are stringent and enforced. To do any work on a sprinkler system in Georgia without a license is a felony. Companies with licenses are published
and so are the names of of all certificate of competency holders and licensed inspectors.
Starting the first of the year all inspectors (must be NICET III) will have state issued photo identification tags to be worn around the neck. Slight modification, inspectors may be NICET II to get a license but must have NICET III to continue beyond the next annual renewal or they are dropped.
We are fortunate to have some really good people who know what they are doing at our state fire marshals office. I wish every state was like this.
Colorado requires 10% up to 100 psi and 10 psi over 100 psi. It is pretty good.
I still see a lot of people (designers and ahj's) who adjust the tested flow as well as the pressure - telling me they really don't understand what they are looking at, or how it works. I wish I had enough money to send all the AHJ's Pat Brock's book on hydraulic's.
FM generally lets you use the tested flow. They test the water supply themselves, and their densities are often different than NFPA's.
The densities and other requirements of the standard include safety factors. The problem is, the standards are all based on maintained systems. Thats a big issue, I think. C-value of 100, on a dry system that hasn't been flushed in decades doesn't really matter. The pipe can be so obtructed from pipe crud that it may not flow at all.
And too many people use a "one size fits all" approach to hazard. A computer room with very high air flow and lots of equipment needs a higher density than one with little equipment. But the systems are usually designed and installed by the contractor with the cheapest price. The owner would rather upgrade the ceiling tiles than pay for bigger pipe and/or closer head spacing. Additionally, a large wide-open space is a bigger problem than a lot of small areas with passive system seperations.
Half of the fire protection professionals out there still think that fire sprinkler systems are designed to put a fire out. I think that since most design basis is containment, a property remote from fire department response warrants larger remote areas or larger safety factors, etc.
The funny thing is, almost everytime someone sends me their calcs because they "can't get them to work." I make some adjustments to their data, and they work fine. I would bet that a lot of the borderline calculations have a larger safety factor than the end result of the calcs indicate. Many designers today just let the computer do it for them - they couldn't perform a hand calc if their job depended on it.
I walked a jobsite a couple of months ago. The building had a 6" loop with 1-1/2" branchlines. It seemed excessive for a 20' high building with 105 PSI on the gauge. I found a set of the drawings. I can't remember everythig exactly, but the gist of it is: The "designer" showed a demand of something like .44 gpm/sqft / 2000 sqft. No problem there, except the heads were spaced at 120 sqft and were 5.6k heads. The starting head pressure was over 85 psi! Ignoring the fact that the spacing exceeded 100 sqft, this designer didn't consider using larger orifice heads. Just kept increasing the pipe size until something worked. System was installed as designed and approved by the AHJ. Safety factor? Yep, in all the wrong ways.
If a good designer wanted to cheat the system, they could. Many AHJ's would not be able to find a deliberate calculation cheat. They focus in on a few numbers and don't even do a basic check themselves. I'm willing to bet if someone left 10% out of the elevation of every Pe loss, it would only be caught 10% of the time. I'm probably being optimistic about it being caught that much here though. Our fire departments are underfunded, understaffed and their plan reviewers focus on all disciplines. I think the best ones just kind of have to know who they can trust. An indication of who to trust would not be the designer who uses every justification to install an inferior system.
20 years from now, we will all be calculating differently.
But for now, my opinion is:
1. Get a good flow test, and adjust it correctly.
2. Have an appropriate safety factor based on the type of system and hazard.
3. Design it correctly.
4. Educate the client and the AHJ if needed.
5. Sleep well at night, knowing that you have protected something other than your wallet.
