June 2007

Tanker Calculations And Pre-Planning Are Critical

By John Clauson

On the fire ground, it’s better to have it and not need it, than to need it and not have it. This was the philosophy imparted to me in Pearl River, N.Y., during my early years in the fire service. The community had hydrants, good ones, at regular intervals and a tanker was a truck with 1,000 gallons of water and drafting was something that was done once or twice a year.

Then, I moved to Unionville in rural Orange County, NY. Twenty-six square miles of town with nothing but ponds and creeks. The village has a water system with hydrants, and when I first arrived, they were pretty bad – certainly nothing reliable for big fires.

Tankers were single-axle, gasoline power jobs with stick shifts and the really fun electric two-speed rear ends. If they had dump valves at all, they were very small. Portable pumps and portable tanks were far and few between. It was quite common in those days to not have enough water for a large fire.

Little by little, things changed, not only in Unionville, but also throughout the fire service in general. Apparatus with 750 gpm pumps were upgraded to rigs with 1,250 and 1,500 gpm pumps. The gasoline apparatus were replaced with diesels, some in excess of 400 hp, and the sticks with automatics.

The evolution continued with tandem axle apparatus becoming more common, more carrying portable tanks, big tanks, big dump valves and then in Unionville, a new water system that kicks butt for fire suppression.

There are so many things our department has today that we take for granted that were not available back then, and the same is true for many, if not all departments.

Consider the difference between the old, hard-sleeve suction hose compared to the lightweight and flexible suction hose today. Ever tried to mate a hard suction line to a hydrant that is not perfectly aligned? Then, there’s the dramatic increase in supply line hose from 2.5-inch to 5-inch and PVC dry hydrants.

Rural firefighters have come a long way and, today, we almost always have sufficient water to fight the biggest fires.

Tankers have morphed from the retired and donated fuel and milk truck, or worse, the Army surplus 6x6 with a tank strapped to it in some fashion, into the powerful and sleek, purpose-built fire tankers found all over rural America.

The objective of these tankers is to bring the right amount of water to the scene, a fundamental in fire suppression. If the right amount of water is brought and applied correctly, structures can be saved. Don’t bring enough, and there’ll be a protracted surround and drown operation and the building will undoubtedly be lost.

Miami-Dade Aerial 2 uses its 60-foot ladder pipe while a crew from Aerial 29 operates a hand line to battle an early morning fire of undetermined origin at a wood-frame office complex that was destroyed March 13. Aerial 2, Miami-Dade’s busiest company and one of 60 units that responded, had been in service a few months. It is one of 15 aerials being delivered by Rosenbauer through a 5-year contract. It has a two-section hot-dipped galvanized steel ladder on a Spartan Gladiator Evolution low-entry cab with a Rosenbauer/General Division heavy-duty extruded aluminum, rescue-style body. It is equipped with a 1,500 gpm Hale Qmax pump with a 500-gallon tank and 20-gallon foam cell. All the ground ladders are stored in the body. It comes with an Onan 10,000-watt generator. The hose beds carry 500 feet of 5-inch, 500 feet of 3-inch and 300 feet of 2.5-inch hose. Two crosslays of 250 feet of 1.75-inch hose are provided, along with a booster reel over the pump compartment. There is also a front bumper line of 250 feet of 1.75-inch hose. Aerial 2, which had a price tag of $620,000 including hose and equipment, logged 10,000 miles in its first five months of service.          (Photo by Ray Bell)

Unionville’s tanker has a 3,000-gallon portable tank and left and right main intake valves (MIV). The apparatus, which also has a Hale 2,000 gpm pump, carries 4,000 feet of 5-inch hose.          (Fire Apparatus Photo by John Clauson)

The Unionville (N.Y.) Volunteer Fire Department designed its 2,500-gallon KME tanker with rear and side dump valves, all capable of flowing water at the same rate. To achieve that, the department sacrificed the rear compartment. Direct fills below the rear dump valve can fill at a rate of 1,500 gpm.          (Fire Apparatus Photo by John Clauson)

There are many formulas to pre-plan exactly how many gallons per minute and total water supply (TWS) will be needed. That same pre-planning needs to happen with tankers. It’s important to know how much each tanker can supply in gpm, not just in the total capacity of the tank. Three basic factors need to be known to determine that gpm value of the tanker: loading time, unloading time and transit time.

To determine the load time, in accordance with the prescribed Insurance Services Office (ISO) performance test procedures, the tanker must travel 200 feet, be filled and then travel an additional 200 feet with the procedure timed start to finish.

It’s important to remember the fill restrictions of the various tank makers. Some polypropylene tanks are restricted to 1,000 gpm, or 100 psi as a fill rate. Fiberglass tanks can accommodate fill rates of 1,500 gpm or 150 psi. To optimize the value of the tanker, it should be filled at the fastest rate possible.

Next, determine the transit time. Planning for this is done at 35 mph. Anything above that speed limit is given no ISO credit.

Then, the unloading time needs to be calculated in a matter similar to the filling procedure: the tanker must be timed, start to finish traveling 200 feet to the dump site, time dumping and then traveling 200 feet beyond the dump site.

Conventional tankers will have 10 percent deducted from the rated load capacity for spillage and under filling.

To put that formula into practice, let’s use a 2,500-gallon tanker being filled at a rate of 1,000 gpm. In 1980 the Insurance Services Office (ISO) established a tanker delivery time and rate of flow test. It was common to estimate one minute for hooking up the tanker fill site supply hose and then one minute for breaking down. This adds two minutes to the overall fill time of 2.5 minutes for a total of 4.5 minutes of ISO-measured “fill time.” Here is where considerable time can be saved today by using Storz quick-couplings and Large Diameter Hose (LDH).

A hypothetical transit route of 2.5 miles from fill site to dump site will equal 5 miles for a round trip. A tanker traveling 5 miles at 35 mph will require 9.5 minutes of transit time.

Next is the dump time and, let’s assign this tanker a dump rate of 1,000 gpm. That means it will take 2.5 minutes to dump the 2,500-gallon load it carries, plus the addition for the 200-foot factor as outlined in the ISO rating procedure. So, the dump time for that truck is 3.5 minutes.

All that added up – 4.5 minutes for filling, 9.5 minutes for travel and 3.5 minutes for dumping – totals 17.5 minutes for one complete loop in this tanker shuttle.

Given the fact that the tanker is 2,500 gallons in this particular scenario, 250 gallons needs to be subtracted to adhere to the 10 percent subtraction for spillage and underfilling, meaning it has an effective capacity of 2,250 gallons for firefighting. Doing further math, that tanker has a value of about 130 gpm in a tanker shuttle, a number arrived at by dividing the 2,250-gallon capacity by the 17.5-minute loop time.

That means five similar tankers in this same shuttle would yield a fire flow of around 650 gpm. One proviso that needs to be mentioned is the fact that ISO allows vacuum tankers to count their full capacity toward the formula, with no 10 percent deduction, because they are closed vessels with no chance for spillage or underfilling.

Improving Fire Flow GPM
There are ways to improve the fire flow gpm, but before discussing those methods, it should be mentioned that rural departments that have an ISO Public Protection Classification (PPC) rating of Class 9 or 8B can only get credit for static water by having a 50-year drought study done and filed with ISO.

With that out of the way, let’s look at ways to improve the previous scenario.

By increasing the fill rate to 1,250 gpm, giving a fill rate of 2 minutes, and shaving an additional 30 seconds from the hook and unhook time by using quick couplings and training will mean a fill time of 2.5 minutes, saving 2 minutes.

Dump And Transit Times
Transit times can be improved by developing additional water sources, closer to potential fire scenes. For instance, a water source one mile from the fire will mean a two-mile round trip. At 35 mph, that will mean a 4.05-minute transit time, saving about 5 minutes from the previous scenario.

Dump times can be improved as well by increasing the dump rate to 1,500 gpm through apparatus design and using techniques such as venting by opening the fill hatches, remote switches allowing dumping from the cab, large tank-to-pump lines if using the nurse pump-off method of discharging water, back-up cameras for easier apparatus placement at the portable tank and the design of the tank itself.

Some manufacturers use a sump design in a fiberglass tank that uses the physics of the weight of the water to help push it out the chute.

Increasing the dump rate to 1,500 gives a dump time of 1.6 minutes and training in spotting the tanker at the portable tank, hooking and unhooking can save 15 seconds off the 200-foot ISO factor, for 45 seconds. That means a total unload time of 2.05 minutes

These improvements translate into a total “loop time” of 8.6 minutes. Translating that into fire flow by dividing the effective capacity of the tanker – 2,250 gallons – by the loop time equals 261 gpm for the 2,500-gallon tanker. With those parameters, a five-tanker shuttle of similar performance would yield around 1,300 gpm in this scenario.

Moving on to another topic, one of considerable discussion in the area of moving water is the nurse tanker versus dump operation debate.

Where I’m from, there are very few locations where portable tanks can be set up next to the attack engine. Our usual scenario is the engine lays 500 to 1,000 feet of 5-inch supply line up a driveway. Most of our neighboring tankers have fire pumps of at least 1,250 gpm. We use a Siamese fitted with a clapper valve at the supply end of the lay. The first tanker pumps off its tank capacity to the engine and the water need is then determined by the size of the fire. A 500- to 750-gpm fire flow can be easily maintained by incoming tankers pumping off into the direct tank fill of the nurse tanker. A tank gauge at the rear of the nurse tanker allows the driver of the incoming tanker to not overflow the nurse tanker. Several short lengths of 5-inch hose allow two tankers to hook up at once to the Siamese for uninterrupted flow as each connected tanker nears empty.

A long hose lay to a nearby water source can be hooked into the siamese, which allows for continued tanker supply until the water source engine is established. Portable tanks can be deployed, using the nurse tanker as a draft pumper – 2,000 gpm in our case – expanding the nurse tanker operation for higher flows. Expanded operations with portable tanks can be a problem on narrow back roads for obvious reasons.

Some departments have no choice but to use portable tank operations because their tankers are water tenders only, meaning they have no pump to discharge the water. In this case, an additional engine would be needed at the portable tank site. If a department has the luxury of room to set portable tanks up next to the attack engine, life is good, and the extra engine would not be needed.

Enhancing Performance
Use of a long hose lay to water supply operations at an area away from the fire can alleviate congestion at the access to the fire building.

There are other ways to enhance the performance value of tankers that are not that expensive, given the total cost of the apparatus, especially amortized over the expected 20-year life of most apparatus.

A large pump is worth considering. For the cost of a couple of extra discharges, a 1,500 gpm pump can be upgraded to a 2,000 gpm pump and a 400 hp engine will power it with ease.

Upgrading the tank to pump line from 2.5-inch to 4-inch will dramatically increase the pump’s discharge volume. Similarly, a 3-inch pump to tank line will allow for rapid filling of the tank if it is filled through the pump.

Main Intake Valve (MIV) primers and auxiliary primers should be considered when specifying apparatus. Auxiliary primers allow for the seamless transition from tank operations to draft. The auxiliary primer fills the suction line with water from draft, and opening the MIV while closing the tank to pump line allows the seamless transition to occur. A manual valve on the driver’s side and an electric valve on the officer side saves some money, although having both electrically operated, especially with a top-mount pump panel, is a good feature.

Safety Factors
A back-up system with a camera on the back and side of the apparatus helps the tanker driver position the truck and adds safety around the portable tanks. A “back stop” bumper, which sets the brakes if it touches anything while in reverse, is an additional safety factor. It might be good to hinge the back bumper of the tanker, especially if the rig is long.

Keep in mind that neither of these two options eliminates the need of a ground spotter.

Remote dump switches allow the driver to deploy the valves and chutes without leaving the cab. Pneumatic valves seem to be a bit quicker than electric.

Pneumatic openers on fill hatches, installed on the fill tower, usually a 10-inch-by-10-inch hatch should be configured to open automatically when the dump valves are activated. Opening the hatches virtually eliminates any vacuum inside the tank while the apparatus is dumping.

Most tanks are vented with a 6-inch round vent that also acts as the over flow. It would be interesting to measure the velocity of the air coming through that pipe with a 10-inch Newton dump valve flowing and the hatch closed.

The rural brethren are finally getting some good tools and recognition for moving water without the benefit of pressurized hydrants.

But good tools and good training are meaningless without a suitable source. Firefighters need to keep the pressure on local governments to require the establishment of water sources as new development moves into rural areas. Fires in these “wood chip and glue” new houses, as they spring up, virtually overnight in increasingly rural areas, grow very quickly and burn very hot.

The closer the water source is to the fire, the more gpm fire flow available. Readily available, reliable and ample water is the only hope of saving anything, as it is a fundamental agent in virtually all fire suppression.

Editor’s Note: John Clauson is past chief of the Unionville Volunteer Fire Department, Orange County, N.Y., and is its current engineer. He has more than 40 years in the fire service and serves as a consultant with the National Fire Services Office in Sylvania, Ga.