LDH SAFETY: IT’S NO ACCIDENT
In May 1993, a small volunteer fire company in Chester County, Pennsylvania, was conducting a hydraulics drill when the catastrophic failure of a largediameter hose (LDH) valve turned a routine exercise into a disaster. Verbal accounts of the incident indicated that one of the company’s pumpers was positioned to receive water from a hydrant through 100 feet of five-inch supply hose. Attached to the left-side pump panel steamer connection was a straight, upright gate valve.
As one member opened the hydrant using the operating nut, the LDH began filling with water. At this point, the valve failed in the area between the gate and the swivel, striking the pump operator. The force of the impact threw the operator several feet, causing critical injuries and permanent disability.
The local police and other government agencies investigated the accident. In an effort to determine what went wrong, the fire company duplicated the conditions of the drill, using an identical valve purchased at the same time from the same manufacturer, and got the same results. The second valve failed in the same area as the first. The cause of these failures has not been completely determined at this time.
Even though it appears that the firecompany used the appliance as intended, the results of the catastrophic valve failure are painfully obvious. Unfortunately, it is too easy to become complacent when working around large-diameter hose. The big, bulky, yellow supply line appears rather harmless. Every firefighter fears crawling down a length of 1 ¾- or 2‘/2-inch attack line to gain control of a wildly flailing open nozzle or butt. When a burst length is encountered, urgent radio messages to “shut the line down” often are heard. On the other hand, when LDH is punctured, it produces a fountain-like stream. In most cases, the leak can be ignored or covered by a salvage cover until the operation is over.
Our sense of complacency, however, is jarred when an improperly locked coupling or appliance fails, unleashing its terror on firefighters and civilian bystanders. In a community in New Jersey this past year, a woman was injured when an LDH supply line became disconnected and struck her during a major fire.
At times accidents are unavoidable. However, you can take precautions to help reduce the likelihood of accidents when using LDH.
OPERATING PRESSURES
Large-diameter hose is hose of 3’/a-inch diameter or larger. LDH identified as “supply hose” has a maximum normal operating pressure of 185 psi and a service test pressure of 2(H) psi. (One exception to this requirement is six-inch supply hose, which should not be used at operating pressures exceeding 135 psi.)
For supply hose to comply with the provisions of NFPA 1961, Fire Hose, the manufacturer must proof-test each length to a pressure of 400 psi without failure. This safety margin is twice the minimum service test pressure of 200 psi.
Even with the service test pressure clearly stenciled on the hose, the mentality that sometimes takes over is “big fire, big hose, big pressure.” 1 was at a multiplealarm fire and saw an inexperienced operator pumping a five-inch supply line considerably over the safe operating pressure. When I questioned his reason for doing this, he replied that the flowmeter attached to the 1.1)11 discharge was indicating a decrease in flow and he was trying to increase it! As a result, all he was accomplishing was pumping a tremendous amount of water out of the relief port on the receiving pumper’s intake valve! This shows a lack of understanding of the flowmeter concept. More importantly, however, the rookie inadvertently was exceeding safe pressure limits to supply water to what he thought was the fire.
This example illustrates another point that most don’t consider. Normal pump operating procedure dictates that you pump to satisfy the highest pressure required and “gate down” other discharges as necessary. Consider a situation in which an engine is pumping at 240 psi to supply several attack lines while simultaneously supplying an LDH feed to another pumper. A flowmeter connected to the LDH discharge would indicate the gpm being supplied, but the operator would not have an indication of when the safe discharge pressure of 185 psi was being exceeded. As a safety precaution, pumpers that use flowmeters exclusively on all discharges also should have either a separate pressure gauge or a dual reading (flow/pressure) meter on the LDH discharge.
WATER HAMMER
Water hammer is a surge of pressure that occurs when a high-velocity flow of water is abruptly stopped, creating a ram effect or shock wave. The pressure exerted during this maneuver can be seven or more times that of the static pressure. As the velocity and flow increase, so do the damaging effects of a water hammer.
In Fire Stream Management Handbook (Fire Engineering Books, 1991), author David P. Fornell writes: “1,500 gpm flowing in 1,()()() feet of hose is equal to 8,508 pounds of water moving at a speed of 17 miles per hour.” Attempting to abruptly stop this flow certainly can cause one of the components, probably the hose, to fail.
Pump operators must operate all valves slowly, especially those with LDH connected to them. I know that when several buildings are involved and the attack engine on scene is calling for water, the “shotgun approach” (both barrels) is used instead of the slow, deliberate action taught in the pump engineers course.
NFPA 1901, Pumper Fire Apparatus, has addressed this portion of the problem on apparatus built to standards after 1991. All valves, suction and discharge, threeinch or larger, must have a mechanism to prevent the valve from changing from fully open to fully closed, or vice versa, in less than three seconds. They are commonly called “slow-close” valves. This addition to the standard should help in instances such as the previous example; however, plenty of the old nonrestricted valves are still in use.
Some quarter-turn butterfly valves common on large intakes can be converted to “slow-close” with the addition of a handwheel mechanism —a worthwhile investment in safety.
-DISCHARGE-SIDE RELIEF VALVES
Another method of protection that must be incorporated into the LDH system is the volume/pressure relief valve. Such safety devices are available as part of most LDH fittings.
NFPA 1962, Care. Use. and Sendee Testing of Fire Hose Including Couplings and Nozzles, indicates that a pressure/volume relief valve with a maximum setting not to exceed the service test pressure of the hose be used on the discharge side of the pump. These valves should discharge to the atmosphere and prevent the pressure in the LDH from exceeding the desired setting. Manifolds, distributor valves, and LDH wyes all should be specified with a relief device incorporated.
(Photos by author.)
The apparatus pump’s relief valve, which circulates excess discharge back to the suction side of the pump, is not adequate for this purpose and does not provide the required protection.
When LDH is used to supply a deluge set. sprinklers, standpipe, ladderpipe, and so on. the safe way to operate is with one of the previously described appliances in the line. Some departments choose to equip the discharge elbow on the pumper with a relief device. When preset at 185 psi, the valve automatically discharges when pressures above the setting are encountered. The valve’s activation is caused by either excessive pump pressure inadvertently being supplied by the operator or the remote shutdown of the LDH, which causes the pressure to increase.
This same type of device can be affixed to the inlet of an aerial unit to provide the necessary overpressure protection when LDH is used to supply the elevated stream.
SUCTION RELIEF VALVES
Another requirement of NFPA 1962 is that when LDH supply hose is used for relay between pumpers, the suction of the receiving pumper must be equipped with a relay relief valve. The valve should be set at not more than 10 psi over the static pressure of the water source or discharge pressure of a supply pumper in relay. Obviously, the lower the setting, the more responsive the relief will be to an overpressure condition. The relief valve must never be set higher than the maximum pressure of the hose used in the system ( 185 psi).
Both Angus and Snap-Tite Hose, Inc., the two largest suppliers of LDH equipment in this country, agree that any incoming LDH supply line should be equipped with a relief device.
Some feel that the pumper’s suctionside relief valve system, required by the current NFPA 1901 pumper standard, satisfies this requirement. This rationale is questionable for a number of reasons. First, the internal relief valve might not respond quickly enough to prevent the water hammer damage produced by the massive flows encountered in LDH use. Second, the suction-side relief valve is installed in the pump’s intake manifold, which places it after any suction gate valve. If the operator inadvertently closes the incoming gate, there is no relief in the line. Third, the pumper’s on-board intake relief valve is required to be adjustable up to 250 psi. with some externally operated.
This is 65 psi over the maximum safe relief valve setting specified for LDH use.
The equipment manufacturers recommend that the incoming LDH valve be equipped with a relief device that will activate before the shock wave of a water hammer can reach the pump plumbing.
Some pumpers are equipped with a standard “steamer to storz” threaded adapter mounted on the pump’s intake and no relief in the system. NFPA 1962 doesn’t address receiving water from a hydrant source, so I can only assume that this is the intended use of this basic adapter. Unfortunately, it also provides an inviting intake for a supply line from another pumper.
The use of an LDH intake relief valve is the safest way to receive water, as it will provide the proper overpressure protection under all conditions.
LOCATING LDH INTAKES AND DISCHARGES ON THE PUMPER
The 1991 edition of NFPA 1901 prohibits any discharge larger than 2Vi inches to be located at the operator’s panel. This requirement safely moves the LDH discharge away from the pump operator. But where do most departments locate the intake valve? Right on the pump panel! As you can see from the example at the beginning of this article, a failure at this location can result in critical injuries or even fatalities.
The reason most give for locating the, valve on the panel is that it allows the operator to adjust the engine rpm while opening the incoming feed line. However, moving the LDH intake away from the pump panel certainly would increase the safety of the pump operator in case of a failure. Some other benefits include elimi-‘ nating a major tripping hazard; protecting against getting wet when the relief valve discharges; and, in colder climates, reduc-. ing the formation of ice around the operator’s position when the relief valve discharges.
Some suction inlets, such as those at front and rear locations, can be remotely controlled from the pump operator’s panel. Most fire service hydraulics “experts* would argue that front and rear intakes are not as effective as the side suctions for supplying water to the pump. Because of! the reduced pipe size and the many turns that the plumbing must make on its way to the pump, friction loss in the piping is increased and incoming flows are somewhat restricted. This is true, but consider the safety and expediency of these locations when used with LDH.
I sing a piston intake relief valve mounted on the front suction with a short length of LDH for hydrant connection allows you to either take a hydrant or safely receive an LDH feed with overpressure protection away from the operator. It also complies with the requirement for the “slow-close” valve specified in NFPA 1901.
If the intake valve is located on the right pump panel, the easiest way to coordinate the transfer from tank to feed is with two firefighters—one to open the intake valve and the other to adjust the pump discharge pressure. If the operator is alone, he could reduce the engine rpm, move to the other side of the apparatus to open the intake valve, and then adjust the discharge pressure as necessary. This would result in a temporary decrease in output pressure but would afford the safety of removing the potentially hazardous LDH from the pump panel for the duration of the operation.
Lxercise caution when mounting an intake relief valve that protrudes past the outside edge of the apparatus. Physical damage could be done and go unnoticed until the valve is used. If you are considering this type of installation on a new pumper, specify that the steamer connection be either recessed in the pump panel or flush-mounted. This will effectively protect the valve from damage. If the valve positioning causes the running board to interfere with LDH, it can be modified accordingly.
STRAIN RELIEF
Large-diameter hose fittings that will be used off the ground should have a sweep elbow incorporated into their design. With this feature, the hose forms a sweeping angle into the fitting, which safely transfers much of the weight to the ground. Coming straight out of the appliance places a great deal of stress on the hose, coupling, and fitting and sometimes results in a kink.
LOCKING COUPLINGS
At a meeting of the NFPA, the requirement for positive locking devices on all new quarter-turn couplings was approved. The effective date of this new requirement was August 20, 1993. Present hose and equipment have been “grandfathered” and are exempt from this requirement. Some manufacturers, however, can supply kits to retrofit couplings presently in use.
This requirement was partly in response to reports of couplings becoming disconnected when the line is charged. A possible cause of the accidental disconnection of LDH couplings is the presence of a twist in the hose. Firefighters should exercise caution when laying and coupling the hose and appliances to ensurej there is no twist in the line.
The use of LDH has increased our operating efficiency tremendously and is considered the best way to move large quantities of water over long distances. Unfortunately, as tragic incidents in Pennsylvania and other locations show, an enormous potential for disaster is present. when LDH is in use. Considering safety when purchasing LDH equipment and practicing safety when using it will help, prevent serious injury to firefighters and bystanders.
Author’s note: Due to pending litigation, the names of the fire company and the valve manufacturer mentioned at the: beginning of this article have been omitted at their request.
