Aerial Ladders or Elevating Platforms—
Recognize Their Strong Points and Limitations
“WHICH SHOULD I BUY? An aerial ladder or a mobile aerial platform?” Many fire chiefs are asking this question. But the answer is not simple. It depends on the needs of the particular city in question.
For the past 85 years fire departments have placed reliance on the aerial ladder as a means of access to the upper floors of buildings. The ladder has also been used as a water tower. In fact, many cities have abandoned the water tower entirely, placing reliance instead on the metal aerial for this function.
Chiefs then faced the problem that fire in a high-value district could tie up most of their aerials when used as water towers. Should a simultaneous alarm occur in a building where aerial ladders would be required, they would not be available. To solve this problem a new type of apparatus was developed — the mobile elevating or aerial platform.
Aerial platforms, however, brought new problems which are special to the fire service. The platform is somewhat unique in that it is one of the few pieces of equipment which was not developed initially to meet the needs of the fire service. Quite obviously in such a process the equipment has shortcomings and represents a compromise of what the fire service really needs and what they are able to obtain.
Survey your requirements
In one midwestem city recently tests were made which included hospitals, apartment buildings and schools. It was found that on buildings where a mobile platform could not reach certain floors, neither could an aerial ladder. The setback of the buildings from the paved area was too great to be reached by either type. In all cases, however, there was a service area at the rear of the buildings where either an aerial ladder or mobile aerial platform could be used.
Tests in another city showed that on two apartment buildings and five hospitals, none could be reached from the front with any mobile platform being manufactured at the time. The setback was approximately 60 feet from the curb line and this precluded any of the available aerial platforms reaching any part of the building. But they could all be reached on all floors with a 100-foot aerial ladder. Obviously the fire chief is buying an aerial ladder.
Platforms better as tower
Where a city has adequate aerial ladders to meet the grading schedule, then the mobile aerial platform becomes a recommended choice for water tower use primarily and rescue use secondarily. The reasons for this are as follows:
- Faster time to get into operation. All of the piping from the inlet Siamese on the truck to the turret is in place. It is only necessary to run hose lines from the pumper to inlets to put the water tower into operation. The minutes thus saved in this operation spell the difference many times between a bad fire and one which is quickly knocked down. This is particularly true in church fires and others where a fast control is essential.
- Greater water capacities with less friction loss and thus less pump pressure required for a given volume. Water capacities of 1,000 gpm to 2,000 gpm are practical and are being used for massive fog application which has made some spectacular fire stops. Two-and-one-half-inch outlets can be provided at the platform so that a ready-made source of water is available at the platfonn to extend lead lines from the platform into upper floors of the building.
- Greater ease of control by firemen operating the nozzle. They have a wider latitude of operation, either lateral movement of the platform or the angular sweep of 45° right or left and 45° above horizontal to 75° below horizontal for nozzle discharge. Included is the ability to change the discharge pattern on the nozzle when required.
On the debit side, the mobile aerial platform does not have rescue capabilities compared to an aerial ladder. First, it is limited by the side reach which at the medium and lower angles does not compare with an aerial ladder. Second, the load capacity of the aerial platform has definite limitations because it always operates as a cantilever or unsupported structure at the outer end.
At the medium and lower angles and supported at the outer end, the aerial ladder has a greater load potential. Because of this feature more people can be evacuated in a given time at a given location by an aerial ladder than by an aerial platform.
Tests at Fort Wayne
In an effort to evaluate the relative merits of the aerial ladder and the mobile aerial platfonn for rescue operations, Chief Howard Blanton and Training Officer Ralph Ellenwood of the Fort Wayne Fire Department, staged a series of tests which are reported in the March 1964 issue of FIRE ENGINEERING, page 197. These tests while interesting are not a criterion of a comparison between the two types of equipment. It must be understood that Chief Blanton was using only equipment which was available in his own department.
First, the aerial ladder was 100 feet as compared with an elevating platform rated at 75 feet. Obviously the time for full extension of the 100-foot aerial as compared to the 75-foot mobile platfonn would favor the platform. Second, the windows selected were at a height which was within the operating range of the mobile platform. Had the test been conducted using the sixth-floor row of windows, the mobile platform would have been useless. Whereas the aerial ladder would have continued to function on all of the windows.
As part of the test at Fort Wayne the aerial ladder pipe was put into operation and also the turret pipe on the mobile platform. The time to put the ladder pipe into operation on the aerial, raising the ladder from the bed and discharging the water was 2 minutes 32 seconds. For the same operation on the mobile platform it was 1 minute 28 seconds.
There were some comments made under the subject of “conclusions,” which are not supported by experience. The statement is made, first, that the reason better time was made on the aerial ladder was that firemen were used in the test. At a similar test held in Winnetka, Ill., a schoolroom of 30 grade school children were evacuated, 24 of them coming down the aerial ladder and only six were evacuated on the mobile platform on two trips. This first indicates that where we have mass evacuation, the greater number of people will be evacuated on the aerial ladder.
On the aerial ladder we can and usually do have a load distributed at least partly over the length of the ladder, unless there are only one or two men on the ladder. On the aerial platform the load is practically all concentrated on the platform, whether it be one or two or more people. The operation at all times of the aerial platform is cantilever, which is not true of the aerial ladder, and which limits considerably the weight on the platform.
The second observation with which we do not agree is the statement, “Elevating platforms have definite advantages for high-elevation rescue operations.” The test at Fort Wayne did not support this as there were areas in the building that the elevating platform could not reach at all. We are referring here to the sixth floor and some rooms on the fifth floor which could not be reached by the mobile aerial platform and that the aerial truck under similar circumstances had no difficulty in covering.
Cold weather problems
Under fire conditions where water tower operations involved use of the aerial ladder and mobile aerial platform simultaneously, with atmospheric temperature near 0° F, the following observation has been made: The turret operators on both types of equipment had to be relieved at intervals due to the extreme cold. Aerial ladder operation did not require a shutdown of water during the exchange of operators. The mobile aerial platform did and in addition, the platform had to returnto the ground to effect the change. During the period of shutdown the fire was observed to “blossom” or increase in intensity and it took some time before extinguishment had progressed to approximately the condition before shutdown.
Ice accumulation creates a weight problem. On an aerial ladder this can be serious.
The mobile aerial platform suffers the same problem of icing due to exposure to spray from nozzles and there have been reports of two units having tipped over due to ice accumulation on the upper boom. To prevent this ice accumulation, a 60,000-Btu gasolinefired heater can be mounted inside the tipper boom to heat the entire length, an advantage the aerial ladder doesn’t have.
Controls and interlocks
A feature of the mobile platform not provided on aerials is that it is equipped with dual controls. One set is on the platform and the other located at the base of the lower boom on the turntable. These controls are so arranged that they can override the upper controls should occasion demand.
Aerial booms and platforms are much heavier than an aerial ladder of comparable vertical reach. Thus, having a concentrated load at the outer end, plus greater weight of the booms, a wider spread of the ground jacks or outriggers is required. These outriggers are more massive than jacks on an aerial ladder and are therefore operated hydraulically.
Due to the greater weights involved, aerial platforms are equipped with safety interlocks provided so that the booms cannot be raised from the nested position until the ground jacks or outriggers have been properly set. Likewise when the booms are in an operating position, the outriggers cannot be retracted until the booms have been lowered to the nested position.
At this point the writer has one pet peeve concerning the designation of the height of mobile platforms (Figure 1). The present practice is to talk about a “working” height, and the platform heights are rated according to this working height. This is acceptable when such equipment is being used by utility companies or street departments for changing lamp bulbs, or in orchards to pick cherries or for some other purpose where the operator reaches up to do his work.
In the fire service, however, such terminology has no place since a fireman is not reaching up into the stratosphere for anything. His work is out in front of him; he is either operating the turret or is aiding in a rescue operation and the index of the height of one of these units should be from the ground to the platform floor.
The National Fire Protection Association and the National Board of Fire Underwriters in Specification No. 19 covering apparatus equipped with an elevating platform, have this to say in paragraph 9021: “The nominal height of an elevating platform assembly shall be measured by a plumb line from the top surface of the platform to the ground with the platform raised to its position of maximum elevation.”
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AERIALS OR PLATFORMS
Continued from page 614
You will notice that a 75-foot aerial ladder exceeds the 65-foot mobile platform at any and all angles and areas of operation (Figure 2). This comparison is valid from a standpoint of economics since the 75-foot aerial ladder truck costs less than the 65-foot mobile aerial platform.
To provide a rather accurate and graphic picture of the relative usability of aerial ladders and mobile platforms, Figure 3 describes the relative areas of operation. You will notice that at an angle of approximately 60°, that is 52 feet above the ground, a 65-foot aerial ladder begins to reach out farther than does the mobile platform. This platform is one that measures 65 feet from the ground to the floor of the platform. At angles below 60°, the 65-foot aerial ladder definitely outreaches the mobile platform. While the platform has a reach out to the side or at any position from the centerline of the turntable on the truck of a little over 40 feet, it does not compare with the aerial ladders at the lower angles.
Figure 3 shows the comparative area of operation of a mobile aerial platform measuring 85 feet from the ground to the platform, an 85-foot aerial ladder and a 100-foot aerial ladder. Again, we have approximately the same relative area of limitation with the mobile platform in this height as we had in the 65-foot height. The same relative difference would exist on a 75-foot mobile platform as compared to a 75-foot and 85-foot aerial ladder.
In discussing the mobile platform’s use in operation with fire departments already having them in service, it was the consensus of opinion of fire chiefs now having equipment that the utility of the vehicles and usefulness in the fire service would be greatly enhanced if the manufacturers would pay more attention to fire service requirements. These desirable features for this new equipment are briefly stated as follows:
- Low overall height to permit housing the apparatus in existing stations without altering the door height or ramp approach.
- Low center of gravity so as to reduce roll on turns and provide a more stable feel to the driver. Also it is felt this would contribute to greater safety in operation on wet streets, and particularly where ice and snow are encountered.
- Reduce friction loss in the piping system so that one 1,000-gallon pumper can be utilized to operate the 1,000-gallon nozzle on the turret. Many of the units in service today have been built with little or no regard to hydraulic losses. As a result, friction loss is so high that a number of cities have had to confine the use of the mobile platform to 500-gpm nozzles, as one pumper cannot supply a 1,000gpm nozzle on these units.
- Maximum reach at the side is extremely important as it affects the usability of the vehicle under many conditions of operation.
The fire service benefits in that all manufacturers are supplying more enclosed compartment space in this new apparatus than ever before provided on standard vehicles.
In conclusion, it is quite apparent the mobile platform has definitely established itself as a desirable and useful piece of equipment in the fire department. It, however, does not entirely replace the aerial ladder as you have noted from the diagrams and the actual building conditions that exist. Each type of apparatus has a use in the fire service. There is little question but that in time important changes will develop in the mobile platform and it will become an even more effective piece of equipment for fire department operation.