July 2007

Firefighting Field Notes

by Dominic Colletti

Five ‘Must Do’ Items When Specifying A New Engine

If you are part of an apparatus committee specifying a new engine, here are five “must do” items that can assist the committee to make better decisions regarding the fire pump and pump-related equipment configuration.

Time invested up front here can pay future dividends in development of an apparatus with increased firefighting capability and reduced equipment maintenance requirements.

At the top of the must-do list is: consider purchasing a “large-body” fire pump if you are part of a rural fire department.

There are many reasons to consider the large body pump, that is 1,500 gpm and up. While they are commonly found in big city and suburban fire departments that have positive pressure water supplies, rural departments should also closely look into specifying a large body pump because it can provide significant benefits during drafting operations.

What is commonly heard, however, by rural departments when discussing the purchase of a large-body fire pump is, “We can’t use a 1,500 or 2,000 gpm [large-body] fire pump. It is impractical since we do not have adequate water supplies.”

To understand this issue in more detail, one of the subtleties of midship pump design today is that most manufacturers offer both small-body and large-body designs.

Discharge ratings of small body pumps usually don’t exceed 1,250 gpm, while the ratings of large-body pumps can exceed 2,000 gpm. The major differences between small- and large-body pumps are the cross-sectional area of the waterway castings and the size of the impeller assemblies.

High-Lift Drafting

To make this as simple as possible, rural departments that need to draft under high-lift drafting conditions and/or that have static water sources with poor apparatus access should definitely consider specifying a large-body midship pump to increase pump performance from draft. The technical reason: vacuum at the impeller eye of a pump decreases as the pump reaches its maximum rated capacity. Thus pump performance, the ability to develop vacuum and draw water into the impeller eye, falls off.

So, if you are a rural department that routinely drafts under high-lift conditions, or needs to use long suction hose lays from the water source to the fire pump, because of the laws of physics a large body pump can dramatically increase fire pump output – gallons per minute.

In one practical test, using 13.5 feet of lift and a 65-foot-long 6-inch suction hose, a small-body midship pump discharged 618 gpm, and under the identical set of conditions a large body midship pump discharged 1,013 gpm. One does not need to be a fire protection engineer to understand what those numbers mean regarding increasing capability to extinguish a much larger volume of fire.

If yours is a rural department, it just makes good sense to spend the extra bucks for the large body midship pump if you are planning on specifying a chassis power plant with the horsepower to drive it.

Put all that horsepower to work, not only in moving the fire truck from point A to B when responding to the fire scene, but also directly at the fire scene to provide higher water delivery rates. It should be mentioned that you could also order a large-body midship pump and have it rated at 1,250-gpm. The bottom line: under challenging drafting conditions, the return on investment of increased water flow delivery rate by using a large-body midship fire pump is well worth the cost.

Second on the must-do list is to consider installing a 4-inch tank-to-pump valve to increase the water delivery rate when operating from tank water.

If you plan to work from the booster tank as an initial water supply and need to reach high, critical application rates for a blitz attack to quickly knock down a structure fire, for some extra bucks – the price difference between a 3- and 4-inch tank-to-pump valve/line – you can approximately double your flow rate from the booster water tank. This can be a really good return on investment. The issue is simple. A 3-inch tank-to-pump valve/line will deliver about 500-gpm. A 4-inch will deliver about 1,000-gpm.

And here’s some food for thought. In some cases an additional tank-to-pump valve can be installed. Installing two 4-inch tank-to-pump valves/lines would further increase gpm capability when working from booster tank water supplies.

Thermal Relief Valves

Moving on, number three on the list is to consider installing a thermal relief valve to protect the fire pump from needing costly repairs.

Have you ever opened a hose line and steam came out of the nozzle? While most know the reasons why this happens (typically “dead-heading” the fire pump), few understand there is a simple solution available to prevent this from occurring under most conditions.

This simple device is called the Thermal Relief Valve or “TRV” for short. This uncomplicated product could be renamed the “pump overheat guardian” or a so-called “stupidity prevention device” to make everyone better understand its benefits.

Thermal Relief Valves are available in several configurations. Simply, they are thermal protection devices installed on the discharge side of the fire pump, as close to the pump impeller as possible. One popular model is the TRV-120. With this model, if the water temperature inside the pump should reach 120 degrees Fahrenheit, the TRV opens which allows water to discharge to the atmosphere through small diameter tubing, usually 3/8-inch.

Foam Systems

The small amount of water discharged allows lower temperature water from the booster tank or hydrant to enter into the suction side of the fire pump impeller to provide cooling, thus preventing steam generation and an overheated impeller assembly.

The TRV can be ordered with a red light for an indication of a hot pump and activation of water to atmosphere. The plastic tube from the TRV discharge is usually installed to terminate at the pump operator’s panel, pointed at the pump operator’s feet. Wet boots remind the pump operator that he or she has failed to circulate water through the pump. When the temperature of the pump cools below 120 degrees, the TRV automatically shuts itself off and water flow out the discharge tube stops.

A repair on an overheated impeller assembly can cost thousands. For just a few hundred bucks, a TRV-120 can be installed. The benefit is not only saving the cost of the repair, but also not having to take the apparatus out of service. That’s priceless. It makes a lot of sense to order as many TRV-120 devices as pumpers in the station and have all apparatus retrofitted with the valves.

Must-do number four might be an obvious one but needs to be mentioned – consider installing a Class A and B foam proportioning system.

One industry estimate says that over 50 percent of new fire apparatus today have some type of foam proportioning system, compared to a much smaller fraction of pumpers in the mid 1990s. This trend is expected to continue and expand.

Will your new pumper have a foam proportioning system? If not, why? Do your people understand the benefits of using Class A foam for ordinary combustible fire suppression including structure firefighting? If not, you may want to provide a training program for your department that focuses on the features, benefits, advantages and limitations of Class A foam.

State of the art today in foam proportioning systems is the electronic discharge side direct injection proportioner. That’s a long name for a foam injection system that is flow based and non-pressure dependant, within its operational limits. These devices make using foam very easy for the pump operator.

One common option found on these electronic proportioner systems is dual foam concentrate reservoirs. This means that two foam reservoirs are built integral to the water booster tank. Typically, one is intended to hold Class A foam concentrate for application on ordinary combustibles, and the other holds Class B foam concentrate for application on flammable liquids. The additional foam concentrate reservoir provides flexibility to apply Class B foam on flammable liquid spills and small spill fires during automobile accidents or un-ignited fuel spills from bulk delivery trucks, for example.

If you go with an electronic direct-injection proportioning system and decide to install two foam concentrate reservoirs, it is a good idea to purchase Class B Alcohol Resistant Concentrate (ARC) for use on flammable liquids.

One of the most popular formulations today is AR-AFFF – Alcohol Resistant Aqueous Film Forming Foam. With concentrate percentages as low as 1 to 3 percent, this product is intended for alcohol type fires and fuel spills. These type hazards are becoming more prevalent considering the expanding use of Ethanol 85 and other alcohol-type fuel additives.

Researching CAFS

If you decide to use AR-AFFF, be sure to consult with the foam hardware manufacturer for its compatibility with a specific system. These foam concentrates are typically fluids that have very high static viscosity. The foam pump and foam system you choose needs to be designed to effectively handle the specific type of Class B foam concentrate you will use.

And last on the list is to look into the benefits of compressed air foam systems (CAFS).

You may have heard lots of controversy in the fire service about CAFS, and you may not believe the claims of how well they work. Your personnel don’t think they can be used for structure fire fighting, specifically, for interior structure fire attacks? If that’s the case, set the record straight and find out the realities of using CAFS, including their limitations.

There is better information available today regarding the advantages and limitations of CAFS, than ever before. Books, videos and departmental training and education programs are recommended.

While only you can know whether your department is ready for CAFS, if you are on a committee specifying a new engine, now is the time to research CAFS.

Remember, CAFS typically do not retrofit into existing engines well, if at all. So, spend the time now in due diligence of examining the technology and deciding if it’s right for your department. The reason to do this now is that it is easier and much more cost effective to integrate CAFS on a new pumper than it is to try to retrofit later on, if you decide a few years down the road that you want to begin to use the technology.

Take a good look at CAFS – you will be glad you did.

Designing a new engine takes a lot of time and effort – but the rewards are well worth it. I hope these “must do” tips have provided food for thought to help your committee to design an apparatus that not only meets, but exceeds the needs of your community.

Editor’s Note: Dominic Colletti is the global foam systems product manager for Hale Products and the author of two books – “The Compressed Air Foam Systems Handbook” and “Class A Foam – Best Practice For Structure Firefighters.” Colletti is a former assistant fire chief in Royersford, Pa. and serves on the technical committee of the National Fire Protection Association (NFPA) 1500 Fire Department Occupation Safety and Health Program. He is an instructor specializing in CAFS implementation.

Large-body midship pumps provide superior performance under challenging drafting conditions. Rural fire departments working with high-lift or long suction hose lay conditions should look into purchasing a large-body midship pump to significantly increase fireground gpm delivery rates.

The Thermal Relief Valve is a relatively minor cost item when installed on a new fire apparatus and can save thousands later on by preventing pump damage. Fire pumps should be equipped with this simple solution to prevent pump overheating and impeller assembly damage.

Electronic proportioners are easy to operate and high-tech – using rotary gear foam pump technology. Coupled to a dual foam concentrate reservoir system, they accurately inject Class A foam and also dispense high viscosity Alcohol Resistant Class B foams. This provides important fire suppression capability for alcohol based flammable liquid fuel hazards, such as Ethanol 85.