subscribe: Posts | Comments

leader

Test the Flow

comments

Strategies for verifying flow effectiveness

By Paul Shapiro
Published Thursday, January 1, 2015 | From the January 2015 Issue of FireRescue

FlowTestOperating handlines in a high-rise fire scenario has its difficulties. Because of their many pressure limitations, fire protection systems in high-rise buildings can create inadequate performing fire streams with obvious consequences. Because of these potential restrictions, the 2½-inch handline using smoothbore tips has been widely used based on its lower operating pressure requirements. The 2½-inch handline is used by many departments exclusively on all fires in high-rise structures, small and large.

If you were to conduct a survey of the departments that do use the 2½-inch handlines exclusively for high-rise buildings, how many do you think have conducted flow tests to back their reasoning for its use? I would venture to say that many departments made their decision based on what others have done or flow tests that were not done correctly. This article shows how to conduct flow tests for high-rise handlines that realistically simulate the performance capabilities of a high-rise fire protection system.

Water Delivery

First, I want to provide a base knowledge for fire department water delivery operations in multistory structures with fire protection systems based on National Fire Protection Association (NFPA) codes. There are two basic sets of standards that have been put out by the NFPA that affect water delivery. The first standard was in place until 1993 and the second standard, which is still in place, began in 1993. Please note that structures with the pre-1993 standards were not required to upgrade to the post-1993 standards.

Pre-1993: The minimum requirement for water delivery is 500 gallons per minute (gpm) at 65 psi standpipe residual pressure at the highest standpipe outlet in the system. The pressure restricting device has a minimum allowed residual pressure at the standpipe outlet of 100 psi. The pressure reducing valve has a maximum static pressure of 175 psi at the standpipe outlet.

Post-1993: The current code requires the same 500-gpm flow but the minimum residual pressure was increased to 100 psi. The pressure restricting device pressure setting of 100 psi is not required and the pressure reducing valve static pressure setting remains at 175 psi.

In a perfect world, a preplan of the buildings in your area should provide the information listed above. Unfortunately, this information is not always available. That is why a flow test of the handline of choice at the standpipe should always be done before fire suppression operations begin. This is done by using an inline pressure gauge at the standpipe outlet and flowing the line to make sure the required pressure is available.

Flow Tests

Many fire service instructors who teach high-rise operations preach the 2½-inch handline and provide flow demonstrations to prove its concept. The commonly used flow test uses an engine company with its pump and discharge to simulate high-rise flow capabilities based on standpipe residual pressures. For them to prove that a small handline, especially a 1¾-inch handline, is ineffective in a high-rise fire, even for a room-and-contents situation, the handline is connected to the discharge of the engine company and throttled up to simulate standpipe residual pressures.

They usually start by using the pre-1993 NFPA minimum standards for high-rise fire protection systems (500 gpm at 65 psi residual pressure at the standpipe). After connecting the handline, the pump operator throttles up to 65 psi on the discharge gauge, which is the simulated standpipe residual pressure.

Here is an example of a flow test that was done using this method. The small handline, 150 feet of 1¾-inch hose with a 100 psi automatic nozzle, is connected, is opened, and achieves a flow measured at 31 gpm, proving its extremely low gallon-per-minute (gpm) capabilities. Next, a 2½-inch handline that is 150 feet long with a 11?8-inch smoothbore nozzle at 50 psi nozzle pressure is connected and opened to illustrate improved flow capabilities with the same 65 psi residual pressure delivering 265 gpm. The flow tests offer proof of the inadequacy of the small handlines based on system pressures (65 psi) and also prove that the 2½-inch handline solves the problem.

Residual Pressure

The abovementioned flow test is not a true reflection of the fire protection system capabilities. Yes, the 65 psi residual pressure is accurate as far as being part of the system rating. However, it is important to remember that the 65 psi residual pressure is based on the fact that the system is flowing 500 gpm. If the system is not flowing 500 gpm, which it would not be with any initial handline, the residual pressure will actually be higher.

Here’s an example of this theory. You have an engine that’s pumping two 2½-inch handlines at 250 gpm each for a total of 500 gpm. Let’s say that after flowing 500 gpm, the intake pressure reads 65 psi. Remember, this is for a total flow of 500 gpm. Then, for whatever reason, one of the 2½-inch handlines is shut down. Now the engine is flowing less water, which in turn will register on the intake gauge by showing more available water reflected by a higher intake pressure. This is the same thing that happens in a high-rise fire protection system. This is why the abovementioned flow tests that are commonly used do not reflect the true performance of the high-rise fire protection system, which in turn creates a false evaluation of the handline being tested.

An Example

The best way to evaluate high-rise handlines is to actually use a high-rise building with its system to create the flows. The following information is based on actual high-rise flow tests conducted at the Binions Horseshoe Hotel in Las Vegas, Nevada, with a 500 gpm/65 psi system.

As you can see with all four handlines that were tested, none flowed 500 gpm and all had a standpipe residual pressure higher than 65 psi. One interesting note, the 1¾-inch handline flowed 188 gpm, which is 38 gpm higher than the NFPA flow standard of 150 gpm per handline.

We were very fortunate to have the Binions Horseshoe Hotel help us with the flow tests. However, having the availability of a high-rise building is highly unlikely. There’s just too many logistics to deal with and possible costs to go with it.

Testing Alternative

There is an alternative in conducting high-rise flow tests that is extremely accurate and easy for any fire department to do. It involves using an engine company and simulating the high-rise fire protection system that you are choosing to test. Let’s use the same 500 gpm/65 psi system that was tested at the Binions Horseshoe Hotel. The equipment needed for this test is as follows:

  •  One engine company.
  •  A minimum of 500 gpm for water supply.
  •  A 2½-inch gated valve.
  •  A flow meter for combination nozzles.
  •  A handheld pitot gauge for smoothbore nozzles.
  •  A 2½-inch inline pressure gauge.
  •  Two short sections of 2½-inch or three-inch hose (10′).

If the engine being used has an electronic governor system, place it in the rpm mode to conduct the test. Steps for the test are as follows:

  1.  Establish a water supply with a supply line capable of delivering 500 gpm. The goal is to flow 500 gpm at the system pressure of choice. Let’s use 65 psi as an example.
  2.  Next, connect the 2½-inch gate valve to the end of the discharge to be used. The gate valve will be used in conjunction with the pump throttle to establish the 500-gpm flow at 65 psi residual pressure.
  3.  After the gate valve, connect one of the short sections of 2½-inch or three-inch hose followed by a 2½-inch inline gauge. The gauge will show the standpipe residual pressure.
  4.  Finally, connect the other short section of 2½-inch or three-inch hose to the inline gauge and the device that is going to be used to flow the 500 gpm. I like to use a water diverter device that has a built-in 1¾-inch tip at 22 psi NP which allows for a pressure reading through a pressure gauge. Note: The 22 psi pressure is unique to this specific diverter. If the flow is to be delivered through a master stream appliance, use the 1¾-inch tip with a nozzle pressure of 30 psi. The flow test seems to be most accurate with the least amount of pressure on the water delivery device as possible.
  5.  After getting the 500 gpm flowing, the 2½-inch gate valve can be gated down to get the required system pressure, again here 65 psi. You will have to readjust the flow once you start gating down the valve to get the required system 500 gpm and 65 psi residual pressure.
  6.  Once this is established, keep the engine rpm and the gate valve at the set position for the 500-gpm flow and shut down the discharge valve on the pump panel. When that is accomplished, you can connect the handline of choice and conduct your flow tests. This setup can be used to test various hose evolutions that would be encountered in a high-rise structure.

It’s important to point out that even with the best quality gauges and flow measuring equipment, the numbers produced in flow tests are not guaranteed to be 100% accurate. As an example, a pressure reading difference of four psi using a one-inch smoothbore tip can make a difference of eight gpm (50 psi vs. 54 psi). A slightly different view when reading a gauge or the positioning of a pitot tube blade in the stream can easily bring about this difference. The difference between a gauge that has two psi increments and five or 10 psi increments can also make a difference. Based on the industry standard, most flow meters have required accuracy rate of plus or minus 5%, and that’s when it is calibrated. With all of this being said, flow testing is a very important tool for developing proper fire streams, so it’s important to use the equipment properly and carefully for best results.

Tool Evaluation

It’s important for firefighters to train and evaluate in as realistic a way as possible. Using the flow test mentioned in this article provides an extremely accurate and realistic way to train and evaluate high-rise handline evolutions. I highly recommend that you evaluate different hose and nozzle combinations based on operations that your department would encounter.

Sidebar – Pressure Regulating Devices

A device designed for the purpose of reducing, controlling, or restricting water pressure. There are two types:

  •  Pressure restricting devices: a device that restricts flow from the standpipe, which, in turn, restricts residual pressure.
  •  Pressure reducing valves: a device that limits the pressure on the downstream water pressure under both static and residual pressures.

Sidebar – Classes of Water Supply Systems

There are four classes of standpipes systems:

  •  Class I: 2½-inch standpipe outlets for fire department use only.
  •  Class II: 1½-inch hose outlets for occupant use.
  •  Class III: Combination standpipe incorporates both Class I and II into a single system.
  •  Combined sprinkler/standpipe system: Incorporates an automatic sprinkler system with a Class I or Class III system.

Comments

comments