Fire Service Ladders and Their Use—Part IX
The Technique of Testing Fire Department Ground Ladders (Wood)
Editor’s Note: This, the ninth in the series of chapters dealing with fire department ladders, ladder evolutions, ladder use and preventive maintenance, is devoted to the testing of wood ground, or wall, ladders. It will be followed at a later date by a companion installment on the testing of aluminum ground ladders.
The information contained in this chapter is taken from recommendations originally made by FIRE ENGINEERING as far back as March, 1923, and contained in all editions of the Fire Chief’s Handbook. Those earlier test recommendations were developed after careful consultation with the manufacturers of fire department ladders and representative fire chiefs, who use them and maintain ladders. They were adopted by various fire service organizations as standard test procedure for the several different types of wood fire service ground ladders then and now in use (these types are described in Chapter 1 of this series). They have been republished in succeeding editions of the Handbook, and in FIRE ENGINEERING, in response to repeated requests. And it is interesting to note that throughout all this time no serious criticism of these prescribed test methods has ever been made; nor, to the best of the editors’ knowledge, have the methods followed at that time, and up to the present, ever proved unsuccessful.
This latter point is made because of the fairly recent publication by the Forest Products Laboratories, Madison, Wis., of a monograph which advocates dispensing with the testing of ground ladders under the caption “Don’t Test That Ladder.” This report has received wide recognition—if not acceptance, by the fire service, because of the high reputation enjoyed by the Laboratories.
If time and space permit, this moot subject will be weighed in some detail in a later installment. In presenting the following chapter, however, the editors wish to emphasize that the test procedures advocated herein, and which have stood the test of time, are believed to be a safe minimum standard for testing such fire service ladders and may be taken as a dependable criterion for the safety of such ladders.
At this time the editors gratefully acknowledge the assistance of representatives of the leading manufacturers of fire service ladders who have checked on these established test techniques and offered their comments and suggestions for possible modifications of previous methods to bring them into line with such slight changes in ladder manufacture as have taken place due to modifications and changes in materials used in such ladders, and methods of their construction.
IN considering the following procedures for testing fire department ground ladders, several points must be taken into account; some of these are considerations which we have already applied to the testing of aerial ladders. Briefly these are: The age of the ladders; were the ladders originally of good make; are they of standard dimensions; to what use have they been subject; and have they ever been repaired (if so for what reason, when, and by whom).
Not all fire departments maintain detailed records to cover all these and other essential data. Nor do all departments attempt to record ladder tests in degree. The practice is recommended, however, and it is never too late to inaugurate it. In addition, as suggested in the chapters on testing aerial ladders, it is advisable to gather photographic as well as other evidence of test results— data which can be taken into the offices of fire commissioners and other authorities, if need be.
These factors have a bearing on the severity of the tests to which ladders should be subjected. At the same time, it should be remembered that ladders, whether old or new, weak or strong, may be submitted to the same stress in an emergency. In view of this condition, it must be conceded that a ladder, if unable to stand up under a fair test, should be discarded. That is one of the prime reasons for testing fire service ladders, to determine which ones are unfit for further use. The question naturally rises; what is a fair test?
What Is a Fair and Adequate Test?
Surely the submitting of a ladder to no more than the stress which it might receive in the course of ordinary usage could not be considered satisfactory. The strength of a ladder decreases with time and usage, and if the ladder is just strong enough to answer ordinary usage at the time the test was made, it is possible that the natural weakening during the period between tests might be sufficient to cause the collapse of the ladder in service during that period.
It is for this reason, as well as to guard against possible excess loads in case of emergency, that ladders should be expected to safely carry more weight in test than they would when used in ordinary fire service.
Since publication of the Laboratory’s report we understand only one manufacturer of fire department ladders has endorsed it, although its broad implications apply more to commercial ladders than fire department products, which are made to greatly higher standards. Test loads applied to a ladder for which that ladder was designed should not show or develop anv deterioration in the strength of the ladder. On the contrary, only by conducting periodic tests of service ladders can faults or flaws which have developed in actual operation be found in time to prevent possible serious accident.
For many years a number of the larger fire departments, some of which have manufactured some of their own ladders at various times, have taken the foregoing into account in setting up the weight limitations permissible, or advisable for testing certain ladders. A number permit only one man at a time on ladders of from 10 to 20 feet in length; two men on ladders from 20 to 30 feet in length; three men on ladders more than 30 feet in length and so on. Some permit as high as six men on 50 and 65foot extension ladders, depending upon limiting factors such as design, type and make of ladder, placement and so on.
In establishing test procedures it has been customary to set the weight of a man at 175 pounds. The weight of a foot of 2 1/2 inch hose charged with water at about 3 3/4 pounds.
Considering first the 65-foot extension ladder, the few that there remain in service being of the solid rail type, if there are four men on the ladder, the combined weight of the men is 700 pounds, without taking into consideration any charged hose lines or other weight.
While it is essential to test the ladder for the maximum number of men recommended as a working maximum, it would be unfair to test this ladder to a maximum load of 700 pounds, for in an emergency this number might be even increased, in addition to the weight of any hose which may be placed on the ladder. The point is—what is the safe and advisable maximum load for testing that ladder.
Photo by the “Detrolt Time”
The usual past practice, and it has been considered a safe one, has been to take the weight of the number of men (on a basis of 175 pounds average weight) permitted on the ladder and test the ladder to twice this weight, not taking into account any allowance for weight of hose.
In the case of the 65-foot ladder therefore, it would be tested to twice 700, or 1,400 pounds. Naturally the load should be evenly distributed along the ladder in units of 175 pounds, the assumed weight of a man, just as good ladder climbing practice calls for safe intervals between men on ladders.
This same basis of testing for a safe maximum, based upon an average weight of 175 pounds per man, has been generally applied to the testing of fire service ladders of all lengths.
This practice is still successfully followed by a majority of the larger departments and there is at present no direct evidence to warrant any serious modification of this formula. However, some departments and fire schools have deemed it advisable to slightly revise these old test maximunis largely in view of the fact that ever since World War II some ladder manufacturers have been unable to secure the same high quality ladder stock that was formerly available, and investigation indicates that ladders are now carried on fire apparatus which contain wood of noticeably inferior quality. This is the main reason some chiefs are revising the limits of ladder loads downward, and making corresponding changes in their test loads.
The following table shows the overload test factors as based upon earlier recommendations and the more conservative limits suggested by one leading manufacturer:
Prior to setting the ladder for test, these items should be checked:
- Make certain that every rung is tight. No ladder should be tested until all rungs are tight. To do so invites failure.
- Check all bolts to be sure they are tight.
- Inspect each rail and rung for checks, cracks and evidence of compression failure. This latter condition may be in evidence by a wavy or wrinkled condition of the grain. It is not easily seen but should be suspected until a careful examination proves otherwise.
When the ladder is satisfactory in all these respects, the test can be carried further.
The first step is to place the ladder in position at the proper angle. Fig. 1 shows a ladder so placed with the location of the loads indicated by arrows (details of loading are described later on). For the 65-foot ladder, the loads should be applied on the 9th rung from the ground, the 16th, 23rd, 30th, 37th, 44th, 51st, and 58th. For the 50-foot extension ladder, apply loads on the 6th. 11th, 16th, 21st, 28th, 33rd, 39th, and 40th rungs (see Fig. 1).
We repeat, if ladder is constructed of highest grade stock the average weight of 175 pounds per person cen be used and the optimum test load made double the normal ladder load.
Applying the Test Load
About the most satisfactory method of applying the test load, and one which does not entail any danger to the men, is to use bags of sand, each individual bag weighing about half the weight of the average decided upon (i.e.: 87 lbs. per bag if the 175 maximum is used). This allows for rope, etc. To each rung on which a load is to be suspended is attached a sturdy clothes line pulley. The pulley is secured to the rung by a piece of sash cord or quarter-inch rope. Through each pulley is threaded a piece of sash cord or quarter-inch rope of sufficient length to reach the ground at both ends.
In the above, “1” is the length of the ladder, measured in feet, “b” is the distance from the base of the building the butt of the ladder should be placed.
Values of “b” for different length ladders is as given below:
The formula for non-trussed ladders is not followed strictly in calculating lengths of short ladders.
One end of the cord through the pulley is attached to one sand bag, as shown in Fig. 2. Then this bag is drawn up into the air by pulling on the other end of the cord. Then the free end of the cord is attached to another bag. as indicated in Fig. 3, after which the second bag is lifted so that the first bag descends sufficiently to keep the second bag clear of the ground. The two bags together should weigh 175 pounds (the rope and pulley included).
This method, if all the cords are threaded through the various pulleys before the test starts, permits adding on the load gradually without endangering the men adding the load.
The bags are suspended as shown in Fig. 3.
The rungs to which the loads should be attached on these ladders are indicated in the following table:
Testing 20to 28-Foot Ladders
While a number of large fire departments permit only two men on ladders between 20 and 30 feet in length, which in test (using the maximum figure of 175-lb. per man) would mean 4 x 175, or 700 pounds, the relative proportion of ladders of this size as compared with the larger sizes, would permit a little greater weight. A test load of 5 men (or 875 lbs.) is suggested by some, for ladders from 20 to 28 feet in length.
Figure 4 shows the placement of ladders during the test.
Straight ladders under 20 feet in length, are tested under four loads of 175-pounds each (equivalent to a total of 4 men).
Extension ladders under 20 feet in length (18-ft., 16-ft., or 12-ft.) are tested under three 175-pound loads (equivalent to three men).
The placement of loads on these ladders is similar to those previously described.
The testing of fire department ladders does not end with the determination of their ability to carry load. The rungs, too, should be submitted to as thorough a test.
The rung of a ladder may be subjected in service to the combined weight of, a fireman and a person being rescued. Assuming the weight of each is 175 pounds the total load of the rung would be 350 pounds. In testing rungs an allowance of 100 pounds should be made as a safety factor, making the total load to which a rung is subjected, 450 pounds.
The usual method of conducting this test is shown in Fig. 5. A block and tackle, using quarter-inch or half-inch rope, will answer the purpose. For the load, the five bags of sand used in the previous tests can be employed. The five sacks will, with tackle, give 450 pounds.
The five sacks are roped securely together. The two ends of a piece of rope 4-feet long are tied securely to form a loop. This loop, together with an “S” hook comprise the method of supporting the load on the rung, as shown in Fig. 5.
The hook one one of the blocks (of the block and tackle) is attached to the “S” hook and the loop of the rope at the center of the rung to be tested. The pull rope of the tackle is then played in until the lower block is sufficiently low to hook to the ropes binding the bags of sand. When these bags are hooked on, the tackle is operated until the bags are clear of the ground.
If it is desired to make the test a little more severe, the bags can be swung from side to side to simulate a moving load such as is encountered in actual service.
Each rung should be tested in a similar manner.
This procedure avoids unnecessary risk to the men carrying on the tests.
After the foregoing tests, the ladder should show no deformation when the test loads arc removed. Any ladder that will not stand this loading without undue deflection, or that takes a permanent set, is questionable for fire department use and should be replaced. As stated, the loadings suggested are less than maximum loadings that ladders should be capable of supporting without signs of undue stress.
Ladders should never be tested by loading them while in horizontal position.