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NFPA 13 '96 Sprink storage tank size?
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(Mechanical)
(OP)
24 Mar 04 16:11The initial comment passed around:
"Site does not appear to have available city water and we will have to use the existing well for Domestic Water. As far as Fire Protection is concerned, there will be a need for a Fire Pump as well as a water Storage tank.
The storage tank needed for this building will have to be quite large and located somewhere near to the Fire Pump building. Initially, the storage tank should be filled via outside water source with a water feed from the domestic line controlled by a float switch will add water as necessary to maintain a minum level for fire protection.
I will need to know the hazard level of the building to estimate the storage tank size. If light hazard, the water demand will be Hose Stream Demand (100 gallons per minute for 30 minutes per NFPA 13 Table 5-2.3) plus the water supply for sprinklers ( .10 gallons per minute/square foot for 30 minutes). If a higher Hazard is considered, the water demand for the Fire Sprinkler System can be much higher than this.
From some quick calculations that I have come up with, we could be looking @ a 70,000-140,000 gallon tank depending on the Hazard level of the spaces. Remember, the tank has to hold enough water to allow the water flow @ a minimum gpm for 30-60 minutes depending on the Hazard level."
Reply to the above:
"The assessment indicated below is correct to the extent that a fire pump and storage tank are required if the building is sprinklered and the city water supply is not adequate to meet the demand. However, I question the tank size indicated in this . I am assuming this is a car dealership with a service facility. The showroom would fall into an Ordinary Hazard, Group 1 occupancy while the repair shop would be Ordinary Hazard, Group 2. The hose stream demand and required duration of supply is the same for both classifications. For Ordinary, 2, the required density and area are .2 gpm/sq ft over a design area of 1,500 sq ft. This will require a flow rate of 300 gpm. The hose stream requirement is 250 gpm. The required duration for this occupancy ranges from 60 to 90 minutes. Taking worst case scenario you will be flowing 300+ 250 = 550 gpm for 90 minutes. Throw in 15% additional flow for safety and this would be 630 gpm. Flowing 630 gpm for 90 minutes requires a total of 56,700 gallons.
I think the authority having jurisdiction may allow a smaller tank. The clients insurance company may also have a say in this as well, therefore the AHJ and insurance carrier should be consulted."
Reading the NFPA 13 is confusing on this issue... we are lacking experience with this as we rarely do fire protection design.
Thanks in advance -
~MX
Replies continue below
(Mechanical)
24 Mar 04 21:42Let's address this in a couple steps:
1 - Will the tank/pump also supply site fire hydrants? If not, then the 250 GPM demand is not to be included in the requirements.
2 - Is there a remote station or central waterflow alarm station? If so, then the smaller duration will be allowed...so you could use 60 minutes.
3 - Since this is an ordinary hazard occupancy, if the ceiling (or deck if exposed construction) is less than 20', then the design area may be reduced per NFPA 13 allowance for QR sprinklers. If your deck is 20' for example, then the design area may be reduced to sq ft.
So, putting this all together, assuming a 20' ceiling/deck, the design area would be 0.20 gpm / sq ft over the most sq ft. This is 225 gpm. Add 15% for overdischarge/inefficiency...you get approx 260 gpm.
If the 60 minute duration is allowed as noted above, then you have a tank size of 15,600 gallons.
HOWEVER, if the tank is to supply the ENTIRE fire demand, you could be looking at some very heavy water demand issues. If you are in UFC land, there is a table in the appendix (I think) that gives you site fire hydrant flow requirements. This could be as high as gpm. Then the tank would be 180,000 gallons.
Feel free to me if you need further clarification or assistance.
(Mechanical)
(OP)
25 Mar 04 09:48Thanks for the reply, it clears up some of the NFPA 13 confusion. To answer your questions:
1 - The tank will need to supply the fire hydrants, so the 250 GPM demand will need to be included.
2 - We will be installing a remote waterflow station, so the 60 minutes could be used.
3 - The ceiling (upper level) and the deck (lower level) are both less than 20'.
Also I noted under 5-2.3.1.3-a that has an area less than sqft, sqft should be used. From this I think the calc for the minimum is:
300+250= 550 GPM
550 + 15% = 633 GPM
Bare minimum (no safety): 550 GPM * 60 minutes = 33,000
With safety: 633 GPM * 60 minutes =
Does this make sense?
Also, if we do not need to put in sprinklers per code but we do decide to for the owner's insurance company, would we still need the storage tank sized to comply with NFPA 13?
Thanks again
(Mechanical)
25 Mar 04 13:32The insurance company will likely require that the system be installed per nfpa.
As far as the tank supplying the hydrants, 250 GPM is the allowance required to be considered with a sprinklered building. However, you may need to consider the site fire flow requirements. For example, many AHJs require a minimum availability of GPM @ 20 psi at any hydrant. This would greatly affect the size of the tank. That issue alone needs to be clarified by the AHJ, as they are seperate and distinct.
If you have a reliable water source underground, you could do a vertical turbine pump to supply the hydrants and sprinkler system. But, there are several other issues to consider when taking water from a "raw" source. We just recently supplied a rack sprinkler system from a vertical turbine pump. The underground water table was about 15' deep and was basically fed by the Mississippi river, so we had a great supply.
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In this installment of QRFS&#; series on the inspection of commercial automatic fire sprinkler systems, we detail the National Fire Protection Association (NFPA) requirements for the inspection of tanks.
Tanks supply water to fire sprinkler systems, in part or in whole. They are often used in rural areas to serve as the entire supply of water, and are also used in structures that have a municipal water supply but must deal with high-demand fires or special circumstances. These include warehouses with high-piled storage, aircraft hangers, and high-rise buildings located in earthquake-prone areas that need a secondary water supply.
The amount of water needed to control or suppress a fire is based on the duration and demand required by NFPA 13: Standard for the Installation of Sprinkler Systems. In many cases, a building will require several thousand or hundreds of thousands of gallons to supply a fire sprinkler system. This is where tanks that augment the main water source come into the picture.
The tank installation standard, NFPA 22: Standard for Water Tanks for Private Fire Protection, permits tanks to be made of steel, wood, concrete, or coated fabrics, and categorizes tanks in three types:
This video shows the installation of a below-grade tank:
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After a tank is installed, connected to the fire sprinkler system, and is in operation, Chapter 9 of NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems covers its inspection requirements. At the beginning of the chapter is a table that summarizes the inspections, testing, and maintenance; most of the inspections are external, but the list does include some internal items that need to be looked at occasionally.
Tanks must be sized to provide enough water to control or suppress a fire in the building, and water levels must be checked and maintained. The water level may be indicated by a device or a visual mechanism. NFPA inspection requirements are as follows:
From the Edition of NFPA 25
9.2.1.1* The water level in tanks equipped with supervised water level alarms that are supervised in accordance with NFPA 72 shall be inspected quarterly.
9.2.1.2 The water level in tanks not equipped with supervised water level alarms connected to a constantly attended location shall be inspected monthly.
The supervised water level alarm is an electric or electronic device that detects changes in the level. When the water level falls below the fill mark, a signal (supervision) will be sent to the fire alarm panel or at a constantly-attended location (a guard shack, an alarm monitoring service, etc.). This electric supervision means that the water level in a tank must only be visually inspected every quarter. If a tank just has a visual indicator, such as a sight glass or a float (such as a pully-style indicator shown below), the inspection frequency increases to monthly.
One of the biggest challenges in maintaining fire sprinkler systems in northern climates is protecting water (and other agents) from freezing. Due to the size of most tanks, they are usually located outdoors. All NFPA water-based fire protection standards (NFPA 13, NFPA 14, NFPA 25, etc.) conservatively increase the water freezing threshold to 40 degrees F, instead of 32 degrees F. This higher temperature is required due to the stagnant nature of water in fire protection systems. NFPA 25 inspection requirements for maintaining 40 degrees F are as follows:
From the Edition of NFPA 25
9.2.2.1 Tank heating systems installed on tanks equipped with low water temperature alarms supervised in accordance with NFPA 72, connected to a constantly attended location shall be inspected quarterly during the heating season.
9.2.2.2 Tank heating systems without a supervised low temperature alarm connected to a constantly attended location shall be inspected daily during the heating season.
9.2.3.1 The temperature of water in tanks shall not be less than 40°F (4.0°C).
9.2.3.2 The temperature of water in tanks with low temperature alarms supervised in accordance with NFPA 72, connected to a constantly attended location shall be inspected and recorded quarterly during the heating season when the mean temperature is less than 40°F (4.0°C).
9.2.3.3 The temperature of water in tanks without low temperature alarms connected to a constantly attended location shall be inspected and recorded weekly during the heating season when the mean temperature is less than 40°F (4.0°C).
Heating systems for tanks vary widely and include steam, gas-fired, oil-fired, coal-burning, electric, steam coil, and solar water heaters that are permitted by NFPA. The objective is to keep water from freezing and creating ice that blocks or plugs the fire sprinkler system. During cold weather, the heating system for the tank needs to be inspected either:
Inspections during the heating season (typically Oct-May in the northern U.S. and Canada) need to verify and record that the water is at least 40 degrees F. Frozen fire sprinkler systems will not protect the building or its occupants from fire, of course.
The exterior visual inspection of the tank is one of the easier, non-technical duties of onsite facilities personnel. If something looks bad, chances are it will trigger the need for some maintenance. Remember, tanks come in all types, shapes and sizes. Some tanks are supported by steel structures that are susceptible to foundation settling or shifting or everyday rust. Some tanks are wood and can experience rot, while for some concrete tanks, cracking is a concern. NFPA 25 outlines the following inspections:
From the Edition of NFPA 25
9.2.4.1* The exterior of the tank, supporting structure, vents, foundation, and catwalks or ladders, where provided, shall be inspected quarterly for signs of obvious damage or weakening.
9.2.4.2 The area surrounding the tank and supporting structure, where provided, shall be inspected quarterly to ensure that the following conditions are met:
(1) The area is free of combustible storage, trash, debris, brush, or material that could present a fire exposure hazard.
(2) The area is free of the accumulation of material on or near parts that could result in accelerated corrosion or rot.
(3) The tank and support are free of ice buildup. (4) The exterior sides and top of embankments supporting coated fabric tanks are free of erosion.
9.2.4.3 Expansion joints, where provided, shall be inspected annually for leaks and cracks.
9.2.4.4 The hoops and grillage of wooden tanks shall be inspected annually.
9.2.4.5 Exterior painted, coated, or insulated surfaces of the tank and supporting structure, where provided, shall be inspected annually for signs of degradation.
Exterior painted and coated surfaces need to be inspected annually to make sure that the tank surface and surrounding structure are still being protected from corrosion. If the tank has a coating that consists of exterior insulation, the insulation needs to be inspected annually to make sure that it is in place and continues to protect the water from freezing.
On a quarterly basis, the supporting structure of every tank must be inspected, regardless of whether it is installed inside or outside. The inspection needs to verify that the structure does not appear to be weakening or damaged. The following items have to be checked:
The interior of a tank contains the water for the fire sprinkler system, of course, which can complicate inspection. Nevertheless, while many interior issues become apparent on the exterior if left unchecked for a long time, it is critical to have a look inside of tanks to catch issues early. The inspection requirements listed below are typically done by a qualified inspector or contractor:
From the Edition of NFPA 25
9.2.5.1.1* The interior of steel tanks without corrosion protection shall be inspected every 3 years.
9.2.5.1.2* The interior of all other types of tanks shall be inspected every 5 years. 9.2.5.2 Where interior inspection is made by means of underwater evaluation, silt shall first be removed from the tank floor.
9.2.5.3 The tank interior shall be inspected for signs of pitting, corrosion, spalling, rot, other forms of deterioration, waste materials and debris, aquatic growth, and local or general failure of interior coating.
9.2.5.4 Steel tanks exhibiting signs of interior pitting, corrosion, or failure of coating shall be tested in accordance with 9.2.6. 9.2.5.5* Tanks on ring-type foundations with sand in the middle shall be inspected for evidence of voids beneath the floor.
9.2.5.6 The heating system and components including piping shall be inspected.
9.2.5.7 The anti-vortex plate shall be inspected for deterioration or blockage.
The frequency of the interior inspection depends on the material that the tank is constructed of and its corrosion protection. If the tank is made from steel and does not have any corrosion protection, such as paint or a corrosion-resistant coating, then the inspection needs to be done every three years. For concrete and wood tanks, and steel tanks with corrosion protection, the internal inspection needs to be done every five years.
The National Fire Sprinkler Association has an online interactive training course &#; Inspection of Pumps and Tanks ITM Series &#; that is a great resource for tank inspectors. In it, former NFSA Vice President of Engineering Ken Isman discusses what&#;s needed for an interior inspection:
In order to conduct the interior inspection of the tank, you either have to drain the tank completely of water, or you need to send a diver into the tank with sufficient lighting to see the tank&#;s condition. If you choose to send a diver into the tank, the diver needs to be certified to dive in confined spaces. This is more than just a certification to dive in an open body like an ocean. Diving safely in confined spaces takes additional knowledge and training. Make sure to conduct inspections safely at all times. When the diver gets down to the bottom of the tank, they may need to move a layer of silt in order to complete the inspection.
Once inside the tank &#; whether it&#;s full or empty &#; visually inspect the following:
Again, all of these inspection items are typically done by a qualified inspector.
Be sure to check out our previous blogs in the series:
Part one: The annual visual inspection of sprinkler heads
Part two: The annual visual inspection of pipe and fittings
Part three: The inspection requirements for fire pumps
Part four: The inspection of signs, gauges, and alarms
Part five: The inspection of fire sprinkler system valves
If you need to buy parts for your commercial fire sprinkler system, check out QRFS&#; selection of commercial fire sprinkler heads, cover plates, escutcheons, and other components and tools, or just use the search bar at the top of the page to find what you&#;re looking for. If you have any questions about commercial fire sprinklers or need help finding an item, give us a call at 888.361., comment below, or fill out our contact form and we&#;d love to assist.
Contact us to discuss your requirements of Fire Protection Water Storage Tanks. Our experienced sales team can help you identify the options that best suit your needs.