Ladders: Guidelines for Selection, Maintenance and Tests for Reliability
features
Staff Correspondent
Nozzle, ax, and ladder—from the time of bucket brigades on badges, plaques, and other insignia—these three symbols have stood for the fire service. The ladder is the one major item carried alike by aerial truck and pumper. It tends to be taken for granted.
But a closer look reveals some uncertainty about the best answers to such questions as:
- How should we select ground ladders?
- How should we maintain them?
- How can we be sure they remain reliable in emergencies?
To begin with, we should consider the materials available for most types of straight or extension ladders. There are four choices: wood, wood-metal composites, all-metal, and glass-reinforced plastic—or fiberglass. Table I summarizes their main properties.
Mystery of truss ladder
Originally, all ground ladders (like aerials for many years) were wooden. Historians kept little track of such innovations as trussed rails. As the late Roi Woolley wrote in 1950, “The exact date of the introduction of the trussed ladder into the fire service remains in obscurity . . . some mystery also surrounds the introduction of the first extension ladders.”
At any rate, almost all wooden ladders used today above 24 feet in length are of trussed design. The object is to save weight. Sixty years ago, a ladder company might include a dozen men. Ten years ago, in the larger cities, the company had five or six men. Today it might have only four or even three. This dictates the lightest possible ladder for the job.
Wood, however, is not a homogeneous material. It has grain, giving it different strength in different directions. It can contain defects, such as knots, or variable growth rate. It shrinks, checks and gradually ages after long service. The old-growth, close-grained hickory or fir used in ladders is becoming scarce. According to several authorities, wood ladders can develop “a lot more problems than aluminum, particularly as they get older.”
Most ladders are metal
For all those reasons, at least 9 out of 10 ladders made today are all-metal. With rare exceptions, the material is a heat-treatable aluminum extrusion alloy, designated 6061-T6 by the Aluminum Association. Such ladders were first introduced to the fire service nearly 50 years ago. However, it was not until the late 1940s that they became fairly common. Metallurgical and manufacturing techniques got a big boost with the World War II tremendous expansion of the aircraft industry.
More recently, many other special alloys have appeared for aircraft or aerospace work. They, too, are light. Unlike aluminum, though, most have two great disadvantages. They are not necessarily extrudable, for one thing. This is the process of forcing the metal, usually hot, through a die, as you would squeeze toothpaste from a tube, to produce a long bar of uniform and often complex cross section which can then be cut into shorter pieces. Ladder rungs and side rails are typical examples. Some metals are so hard, or brittle, that extrusion won’t work.
A second drawback to these alloys is their high cost. What the defense budget can afford for a fighter plane is beyond the means of a fire department.
The metal-wood composite truss ladder is little used. It retains one deficiency of the all-wood ladder—the rails are still subject to splitting—but it does have lighter weight plus less electrical hazard. Availability of quality wood remains a manufacturing limitation.
Fiberglass gaining
As for fiberglass, it is “catching on,” according to one manufacturer. The rungs remain aluminum. The plastic rails won’t conduct electricity, nor will they shrink or otherwise age like wood. They will, however, crack like wood when overloaded. Not offered in truss construction, these ladders are not available beyond the 24-foot length.
In considering ladder weight, one should take into account the manufacturer’s ladder load capacities. Differences from one material to another may not be as great as the above paragraphs have implied. With good truss design plus proper rail shaping, it is possible to provide strength-to-weight ratios using any of the materials efficiently. See Table II.
In choosing any engineered product, particularly where lives may be at stake, the user needs as complete a definition as possible of the job the product must do. For ground ladders, this would involve agreement on the load-carrying ability and other service conditions for which a “standard” ladder should be designed. Some effort has been directed toward that agreement, but much remains to be done.
Standards for ladders
Moreover, there needs to be a standard governing the design and testing of the product to do that defined job. Such a document does exist for ladders—NFPA Standard No. 1931, 1975 edition. Manufacturers are working to it.
Other agencies besides the NFPA are concerned with ladder design. One of the more useful references is the “Standard for Portable Metal Ladders,” No. A 14.2 of the American National Standards Institute (ANSI). The American Ladder Institute, the Consumer Product Safety Commission and OSHA are also involved to some extent.
Ladder manufacturers have seen the need for better standards.
As one of them has said, “Many years ago we had assumed that the fire departments knew what they wanted. If they wanted a stronger model ladder, they would ask for it. But we are realizing now that the fire service had not been fully aware of how to specify its needs. We have dropped our light models because it’s foolish to continue to offer ladders that can’t carry four or five men.”
Aluminum ladders
Aluminum ladders in general are well designed and constructed. With proper care, they last indefinitely. The first one ever made—in 1930—is still in active service. Manufacturers have elaborate quality control programs. One firm tests at least one length of every model produced at least once a year, loading it until it collapses.
“If it carries 900 pounds when laid flat, we know that when raised it will carry that load with a huge safety factor,” said an official.
In his shop, other tests are made continually, including checks of material hardness as it comes from the supplier. Certified reports are made out on every lot.
“We are on the road,” he continued, “trying to make the user aware of what he is getting. The more information we can give the user, the better off we all are.”
Three objectives
The problem is that ladder handling must usually be taught with three goals: First, lifting, carrying, raising, and climbing so as to assure the safety of personnel. Second, safety to the ladder or other equipment. Third, standardization—the same practices for everyone so men can work smoothly in teams no matter what their company assignment.
Like any other fire service tool, ladders must sometimes be abused when personnel safety comes first. Exposing ladders to flame, dropping them from roofs, putting too many men on them and having them struck by falling bodies are all examples of sometimes unavoidable misuse. Hence, careful inspections and testing become even more important to ensure that a ladder will be safe to use the next time out.
During 1950-52, Fire Engineering published probably the largest body of material on a single subject ever featured in the magazine, “Fire Service Ladders and Their Use.” Most of it dealt with proper carrying, raising, and climbing. That has changed little since.
Ladder maintenance
One segment dealt with ladder maintenance. As the author wrote then: “A considerable percentage of known ladder failures in operation …. is traceable to failure in preventive maintenance.” He made these suggestions:
- Inspect ladders frequently and thoroughly.
- Keep accurate records of every ladder in service, noting all major inspections, tests and repairs.
- Get complete maintenance recommendations from the ladder manufacturer.
- Carry the ladders properly on the apparatus: make sure clamps are tight, guides are lubricated, trays kept clean and dry, compartments are buffered, and locking pins are kept in place.
All this remains excellent advice today.
Examination of ladders
Here is a pertinent quotation from one metropolitan fire department’s training manual:
“Ladders should be examined for alignment of beams, twists or bends, loose rungs, dents or damage to rails, loose or sheared rivets, and any deteriorations in the channels or T sections where openings in the metal may permit accumulations of foreign matter or moisture. Ladders should be thoroughly washed and a light lubricant applied to the slide areas. The halyard or cable should be inspected for wear and replaced when necessary. Check for pieces of glass in channels to prevent hand injury.”
This cleaning and inspection is prescribed weekly as well as after each use. Further checking by the department shop is required if a ladder has been exposed to heat or any “undue stress and strain.”
Recommendations
Aluminum ladder manufacturers add these further recommendations:
- Cable inspection: Running a gloves hand over wire rope halyards to check for broken strands is all right as far as it goes. But you should also check the cable tightness to be sure the cable is not stretched or the pulley mounting distorted. Put the ladder in its fully closed position with the upper section locked. The cable should not be “limp.”
- Sliding lubrication: The best material for this is paraffin or candle wax, applied at least every three months. Use it wherever there is contact between rungs, guides and rails, particularly in the fly section. Put wax on the bottom sides of lock fingers and hooks to allow them to slide easily over rungs. If you use a light oil instead of wax, it will quickly be absorbed or rubbed off, leaving unlubricated aluminum surfaces which can easily seize or gall.
Having done everything possible to take proper care of the ladder, the user must next be concerned with ladder safety. Growing emphasis on product safety is affecting all phases of manufacturing and technology throughout the nation through consumer protection legislation at various levels, the advent of OSHA, and in new legal rulings on negligence or “strict liability.”
Ames Precision Machine Works photo
Newage Industries, Inc., photo
Testing procedures
Whatever the design standards, how can a fire department be sure they are still being met by a ladder after it has been severely handled during a fire emergency? Will it still be safe to use? Recent studies provide some answers. However, many ladder users are not yet fully aware of the available procedures and there is some disagreement about their validity.
When most ladders were wood, safety checks were few and simple. Look for cracks. Tighten stay rods and bolts. Breaks were fairly obvious. Once a rail was broken or burned it had to be replaced. Large fire departments, as in New York City, had carpenter shops to rebuild ladders.
When aluminum took over, however, there was a general feeling of security. The material could not crack, split or rot. Experience with other metal tools indicated that if overloaded, the ladder would bend or break. Severe overheating might cause melting. Just as with wood, such defects would be obvious and call for replacement. The new problem of electrical shock hazard was understandable. It was only necessary to stay out of contact with live circuits, although under fire conditions that wasn’t always possible.
Exposure to heat
By the 1970s, metal ladder failures of an entirely unexpected type began to concern fire officials in several states. Bill Clark, a former battalion chief in New York City who later was director of fire in Prince George’s County, Md., described one incident which highlighted the problem:
“A ladder was exposed to heat coming through a window at a fire. The metal was discolored, so we sent the ladder to the National Bureau of Standards (whose laboratories were only a short distance away). Their tests showed that, not only was the ladder seriously weakened, but the alloy would not stand more than 400°F without damage.”
Since fire ladders can’t be kept from occasional exposure to fire involving temperatures four times the 400-degree level, this was cause for great concern.
Is heat exposure common? In many urban fire departments, yes. An officer of one large eastern fire department has said that “it melts the tips off approximately 12 ladders per year.” Again, that kind of damage is obvious. Less obvious is loss of strength which leaves the ladder unsafe though apparently unharmed. It cannot be too strongly emphasized that, unlike most potential hazards to wood ladders, dangerous loss of strength in an aluminum ladder cannot be detected by any kind of visual inspection alone.
Fiberglass ladders are expected to retain design strength under heat exposure because, like wood, the material may only be affected at the surface. ANSI Standard A14.5 indicates a 30 percent loss of fiberglass strength at only 150°F, but it would take a great deal of exposure to heat the entire ladder structure to a dangerous level.
No temperature limit
Contrary to some opinions, NFPA 1931 specifies no particular temperature limit for ladder material. But it does stipulate a minimum strength for such material—a figure easily met by 6061-T6 alloy provided it has not been overheated in service.
This alloy is an age-hardenable material. That means that its original high strength results from heating the extruded parts at a controlled high temperature for a number of hours prior to the construction of the finished ladder. If the ladder later gets much hotter for even a short while, that strength is dramatically reduced. The metal won’t melt (that takes 1200 degrees). It may or may not discolor as in Clark’s example. Nevertheless, it will have lost so much strength that even a normal load can cause its sudden collapse. Figure 1 illustrates this weakening.
After the Maryland incident, technicians at the National Bureau of Standards (NBS) Fire Technology Division began an intensive study of the problem. They examined two damaged ladders in detail. One was a 35-foot, two-section extension ladder that had failed abruptly when a fire fighter started climbing to assist a second man at the top (who was seriously hurt when the ladder collapsed). The second failure involved a three-section 35-footer that collapsed during a training exercise; no one was injured.
Conclusions of study
Results of these NBS studies appeared in the 73-page 1974 report No. 833, “Fire Department Ground Ladders—Results of a Preliminary Study.” Summarizing its major conclusions:
- The existing NFPA Standard 193 (sic) did not adequately define ladder load-carrying capability. Also, tests specified to prove that capability weren’t really suitable.
- Regardless of the standard, ladder performance requirements did not seem fully defined. Materials used, dimensional uniformity, rung spacing, and resistance to twisting all needed further study.
- Ladder users needed better field testing methods to be sure their equipment was still safe. It was found that a relationship existed between surface hardness of the aluminum alloy and its strength so that simple hardness tests could serve to judge ladder safety after exposure to heat.
In 1975, most NBS recommendations in category 1 above were incorporated into NFPA 1931, a major revision of 193. In category 2, conclusions were naturally involved with manufacturers’ design practices, economics, and a better determination of what the service required. Here, unfortunately, there will probably always be lack of complete agreement.
One manufacturer put it this way: “I feel that the fire industry today does have need of more advanced materials and designs in fire department ladders; however … no one has adequately defined the parameters under which this equipment must function.”
Guidelines lacking
To quote another comment made recently to the NFPA, “The standard lacks the guidelines by which a manufacturer can design, build, or testa ladder against specific performance requirements.”
Although many fire departments may be aware of possible problems with aluminum ladders, as yet few are doing anything about it. Observers have noted some downright dangerous practices by users.
Said one, “They just don’t understand aluminum. They take a ladder blackened by fire, just steel-wool it, and put it back in service. Some people even weld on them.”
It’s not hard to imagine from figure 1 what the application of welding heat could do to ladder strength in the welded zone.
What, then, are the manufacturers doing? First, in light of the changes made when NFPA 1931 was issued in 1975, as well as the recent rise in negligence liability, the “light duty” ladders once available are disappearing. But what is a “heavy duty” model? ANSI standards say the type I heavy duty ladder is rated to support 250 pounds. Obviously this is a one-man capability only, adequate for general industrial use. Is it adequate for the fire service, where rescue work requires ladders to support two or more persons?
In trying to answer that question, the NBS tested three typical two-section aluminum ladders. Table III shows some of the results. As the NBS report concluded, “all three ladders qualify under the ANSI criterion for a heavy duty type I ladder . . . However, note that the ladder of manufacturer A does this with a considerably wider margin of safety.”
Second, to reevaluate those safety margins, ladder manufacturers and the NFPA have begun surveying ladder users to find out what their needs really are. The NFPA survey contains 11 items, which were reprinted in a 1978 International Society of Fire Service Instructors (ISFSI) newsletter. The questions included:
- How much weight must a ladder support?
- How much heat must it resist and for how long?
- How much impact must a ladder be able to withstand?
- How often are users willing to test their equipment?
Other questions concerned ladder dimensions and weights, costs and standards. Replies have been solicited by Samuel Cramer, chairman, NFPA Ground Ladder Subcommittee, c/o Aluminum Ladder Co., P.O. Box 5329, West Darlington Street Extension, Florence S.C. 29502.
So far, few replies have been received. The subcommittee is not prepared to publish them, but they do show that the fire service finds it difficult to define the problem. Just as there is no one exact way to extinguish a fire, so there seems to be no universal agreement on what a ladder must withstand.
There has been agreement that impact resistance should be specified. One person suggested, as the basic requirement, the impact load of a person falling one story and then striking the ladder. Such loading has had little or no investigation and a given moving weight striking a ladder can have much more damaging effect than a greater stationary weight resting on the ladder. This is a subject for research.
There are a few experiments going on with heat-sensitive labels on ladders to indicate the temperatures to which ladders have been exposed. Such investigations, however, can be both time-consuming and costly.
As one ladder company executive has said, “It is not practical for any single company to undertake a major research program and there seem to be no funds available through the public domain for such programs.”
In September 1977, the ISFSI published a brief article titled “Ladders … There Must be Something Better,” highlighting some of the issues discussed here. After some ladder failures in Massachusetts, that state’s fire chiefs association corresponded with Howard Tipton, then administrator of the National Fire Prevention and Control Administration, who agreed that the administration’s fire services technology development group should “review both the subject of aluminum ladders and the present standard …” The ISFSI asked that all available information on ladder failures be sent to the NFPCA. Whether or not the latter group’s reorganization will affect this ladder review remains to be seen.
What about the field testing procedures, category 3 of the NBS recommendations? Says paragraph A-8-1.2 of NFPA 1931, “Departments using aluminum ladders should consider obtaining a hardness test of the material after its subjection to heat.” Revision of this standard, now under way, is expected to make this recommendation stronger and more specific.
How much heat? Enough to make water sizzle or steam? You can’t always tell how hot the ladder was, so when in doubt—test it.
Hardness testing
For a long time, an obstacle to such testing was the lack of generally available data relating hardness to strength for the aluminum alloy generally used in ladders. The NBS report provided such data, see figure 2.
Several hardness test procedures are outlined in standards of the American Society for Testing & Materials as well as by ANSI (Standard Z115.6 is one). These involve using a calibrated force to press or “indent” a small hardened metal or diamond point of precise shape into the surface of the material being tested. The testing device measures how deeply the point penetrates. This is translated into a hardness number. There are various hardness scales for different materials. A very soft metal would not be suited to the deep penetration produced by a force needed to get the proper indent on hard steel. At least eight firms manufacture portable hardness testing instruments usable on aluminum ladders. These can be set up in the shop or taken to a fire station for use there.
Data shown in figure 2 had been difficult to get prior to the NBS study. Ladder manufacturers do not make their own extrusions, but get them from basic aluminum suppliers, who either do not have the data or choose not to make it available.
Hardness test weakness
According to safety instructions issued by one maker of aluminum ladders, “hardness of metal alloys [is] in direct relationship to their temper. Lower than recommended [hardness] readings indicate annealing of the metal and the ladder should be replaced.”
Recently, extensive research by the National Testing Corporation, long known for its work in certifying aerial ladder condition, suggests that hardness alone is not the sole indicator of alloy strength.
“We started looking into this about five years ago,” said a spokesman. “We bought hardness testers and went out and tested a lot of 6061-T6. Our results show that special testing of both hardness and electrical conductivity is needed to really be sure of the metal’s condition. Hardness alone is good, better than nothing, but it is possible to get high hardness readings on material which is weak.”
Conductivity testing, unlike hardness testing, requires expensive and sophisticated equipment. So it seems unlikely that fire departments can be expected to go beyond hardness alone.
All testers not suitable
Not all testers on the market are suitable for use with aluminum. Some are built so they may not fit over the rails or rungs of certain ladder designs. Others may need periodic recalibration. Make sure you know what you are getting. The prices range from under $250 to over $2000, with the average being about $700. So far, only a few fire departments have embarked on hardness testing programs.
One large department, with about 250 aluminum ground ladders in service, does no testing.
Said the deputy chief in charge of the department shop, “We do only rung replacement. If beams are obviously bent, or twisted out of line, we scrap it. We repair about 100 a year, mostly damaged by dropping, but we do lose a few 18 to 30-foot ladders annually—plus five or six 14-foot roof ladders that burn up.”
The load testing procedures of NFPA 1931 are cumbersome but require no such special instruments. However, the user cares less about learning if a ladder meets specs—some arbitrary rating standard—than if it still has the strength it had when new. Is the original safety factor still there? You can determine that accurately only by applying more load until the ladder begins to collapse. At that point, you have your information—but you also have to replace the ladder. This is even more true of load tests on wood or fiberglass ladders. This is the drawback to a destructive test. It proves ladder condition, but destroys it in the process.
Better standards needed
What does the future hold for ground ladder design? It appears that the greatest challenge for standard groups and manufacturers is to arrive at better definitions of the required performance of ladders—in short, a functional standard everyone can live with.
This could answer the objection recently made to the NFPA ground ladder subcommittee about Standard 1931: “A ladder constructed to just meet the testing requirements of this standard would not provide adequate safety while in service.”
To do this will require broader input from the fire service. It is the ladder user who must make his concern for safety felt through his original equipment specification plus his care and use of the product. Full exchange of experience and recommendations among user, manufacturer and standards organizations is a necessary step in the search for tomorrow’s ladder improvements.