By Michael Wilbur and J. Gordon Routley
Have you ever noticed that the rungs of European aerial ladders are spaced closer together than their North American equivalents? Probably not, but if someone made that observation, would you wonder why and whether it makes a significant difference? Interesting questions!
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A recently released study by the National Institute for Occupational Safety and Health (NIOSH) has produced some thought-provoking information related to this subject. It concludes that we should seriously consider reducing the standard rung spacing of our ladders.
Rungs: North America vs. Europe
An astute firefighter first presented the question to NIOSH, observing that climbing aerial ladders is difficult enough when wearing full protective clothing and self-contained breathing apparatus (SCBA) and carrying equipment, but it is even more strenuous for smaller firefighters and those with shorter legs. He had also made noted that there is a significant difference in the rung spacing between European and North American aerial ladders. He thought that narrower rung spacing could possibly reduce exertion and improve firefighter safety.
He took his questions and observations to the team at the Protective Technology Branch (part of the Division of Safety Research at NIOSH), the nation’s leading center of expertise in occupational ergonomics and anthropometry, essentially the science of matching workers and their bodies to their tasks and work environment. This group also produced the anthropometric study of American firefighters in 2015, which is providing a wealth of information on firefighters’ body dimensions for apparatus, equipment, and protective clothing manufacturers. He was able to convince them that the ladder design issues deserved their professional analysis and scientific study. Their recently published report is extremely thorough and based on valid scientific principles.
Ladders are among the fundamental tools of the trade for firefighters. Most of us are very familiar with ladders. We are so familiar with them that we probably don’t give a lot of thought to some of their basic characteristics. We tend to simply accept them as they are constructed.
The dimensions of North American aerial ladders are specified by National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus. The standard requires the ladder rungs to be evenly spaced but allows for that uniform spacing to be anywhere within a range of 11¾ to 14 inches. Almost all North American aerial ladders are constructed with rungs spaced close to the 14-inch maximum.
The standard for fireground portable ladders, NFPA 1931, Standard for Manufacturer’s Design of Fire Department Ground Ladders, establishes almost identical requirements. The rungs must be evenly spaced and the allowable range is from 12 to 14 inches. These ladders also tend to be constructed with rungs spaced at or close to 14 inches.
The equivalent European standards are expressed in metric measurements, but after conversion they also allow for a range of approximately two inches between the minimum and maximum rung spacing. The difference is that the maximum rung spacing is 305 millimeters (mm), which is extremely close to the 12-inch minimum rung spacing for ladders built to NFPA standards. Although North American standards allow for rung spacing of 12 to 14 inches, the European standards allow for a range of 10 to 12 inches.
Almost all ladder manufacturers appear to have adopted the maximum permitted rung spacing in the standards. A typical European firefighting ladder has a rung spacing of approximately 12 inches, while a North American ladder generally has rung spacing of approximately 14 inches. Is that a significant difference?
Simple mathematical calculations tell us that a firefighter who climbs 70 feet on a European ladder would take 70 steps, while the equivalent climb on a ladder designed to NFPA standards would involve only 60 steps. From a user perspective, the difference boils down to lifting a leg 12 inches 70 times vs. 14 inches 60 times. The wider spacing means that each step requires more exertion and places more strain on muscles and joints.
It is also interesting to note that North American industrial ladders typically have almost the same rung spacing dimensions as European fire service ladders. The wider rung spacing that is permitted by NFPA standards is the exceptional case, and it has been this way for decades. The 14-inch rung spacing was a fire service choice at some time, and it was probably incorporated into the NFPA standards before most of us were born.
The Leg Lock
Based on the recollections of fire service historians and amateur anthropologists, it appears that the wide rung spacing was adopted to allow for firefighters to execute a leg lock when working on a ladder. A leg lock is accomplished by passing one leg between two rungs and then hooking the foot on the beam or the rung below. The two extra inches between rungs allow for this maneuverer to be executed more easily (photo 1).
This caused me (J. Gordon Routley) to think back many years to my probationary firefighter training, when I struggled to demonstrate my ability to accomplish this task while wearing ¾-length rubber boots that weighed about 10 pounds each and fit my feet like a pair of buckets. After climbing about 40 feet, I had to hold onto the beams with both hands, stand on one foot, lift the other leg and insert it between two rungs, then bring the foot back so that it was securely hooked around the next lower rung—next to the foot that I was standing on. I was never much of a contortionist.
(1) A firefighter demonstrating a leg lock on a portable ladder. The advent of ladder belts and personal harnesses has made this tactic all but obsolete. [Photo courtesy of the College Park (MD) Volunteer Fire Department.]
Accomplishing the leg lock was a struggle, but there was no doubt that it was an effective means of securing a firefighter to a ladder. With one leg securely wrapped around a rung, a firefighter could confidently perform tasks that required the use of both arms, such as directing a hose stream into an upper-floor window. There was very little risk of falling off the ladder.
As much as I remember the challenge of successfully accomplishing a leg lock, my reminiscences tend to focus more on the process of releasing myself from this secure position, after the locked leg had become numb and the other leg had been supporting my weight for several minutes.
Also, back in those days, I knew a firefighter who was on permanent light duty with a very evident limp. Some years previously, he had been at the top of an aerial ladder with his leg locked around a rung. One of the jacks slipped on the icy pavement and the truck overturned, causing the ladder to fall to the ground. He was fortunate to be extricated without having his leg amputated.
I am pleased to report that the last time I performed a leg lock on a ladder was during that initial training, when the objective was to prove that I could do it. Looking back over a long career in the fire service, I cannot remember a single time that I saw anyone actually use a leg lock on a ground ladder during an operation. It is not, and never was, appropriate to perform a leg lock on an aerial ladder. Safety belts and harnesses have successfully eliminated the need to perform that uncomfortable exercise. If the leg lock was the only reason for the two extra inches of space between rungs, that justification has probably expired.
Figure 1. Ladder Rung Spacing
Source: NIOSH, June 2022. Inset photo courtesy of Emily Renner and the Granville Volunteer Fire Department.
NIOSH Research
The NIOSH researchers were unable to find any other logical reason for the wider rung spacing. Their scientific analysis indicates that 12-inch rung spacing would be considerably more user-friendly because the physical effort associated with each step would be reduced while the climbing efficiency and safety will be improved. The comprehensive analysis is well documented, including close observations and measurements of several firefighters using an instrumented ladder model with adjustable rung spacing. The scientific evidence is well documented in the NIOSH study (Figure 1).
One of the significant aspects of the study was to look at how the rung spacing impacts male and female firefighters with different anatomical characteristics. The advantages of reduced rung spacing would be more evident to firefighters with shorter legs than to those with longer legs, but there is no indication that anyone would be disadvantaged by a change. With diversity and inclusion in the fire service, we have to make allowances for a wider range of physical characteristics.
The rung spacing is also much more significant when climbing a ladder that is close to vertical and, of course, the longer the climb. Aerial ladders are used at angles that vary from almost horizontal to almost vertical, depending on the situation. The advantages would not be as significant when climbing a ladder that is positioned at an angle of 45°, but they would be very evident to a firefighter who is climbing to the roof of a six-story building on a ladder that is positioned at an angle of 70°.
The study should be closely examined to determine if the time has come to make a change in the standards for ladder design. The analysis closely examines the effects of rung spacing on muscle and joint stress (climbing physical effort), climbing speed (climbing efficiency), and the risk of tripping (climbing safety) to reach the same conclusion. There is sound evidence to suggest that we should at least give close and careful consideration to making a change to the NFPA standards that have been fixed for decades on dimensions that were considered to be appropriate when they were adopted, before any of this science existed.
Resistance
We should always expect a certain degree of resistance to proposing a change in an NFPA standard—i.e., “If it ain’t broke, don’t fix it”—but never having given this subject much thought or scientific study does not mean that it isn’t significant. We should not allow traditional fire service resistance to change to stand in the way of seriously considering the potential safety benefits of this proposition.
We can also anticipate that the manufacturers of aerial ladders will not be enthusiastic about redesigning their products to reduce the rung spacing, but it would be reasonable to expect them to incorporate the change when they develop new products or make significant updates. The first one to offer a ladder with reduced rung spacing would be sure to promote it as an important advancement and unique feature. Adjustments in the design of ground ladders would probably be more easily accomplished.
In the end, the users should be defining the requirements and the fire service should seriously examine this impressive research that has been conducted for our benefit.
References
Hsiao H, Whitestone J, Kau TY, Whisler R, Routley JG, Wilbur M. (2014). Sizing firefighters: Method and implications. Human Factors, 56, 873-910. https://doi.org/10.1177/0018720813516359.
Simeonov P, Hsiao H, Armstrong T, Fu A, Woolley C, Kau T-Y. (2020). Effects of aerial ladder rung spacing on firefighter climbing biomechanics. Applied Ergonomics 82, https://doi.org/10.1016/j.apergo.2019.102911.
MICHAEL WILBUR is a 31-year veteran of the Fire Department of New York, from which he retired as a lieutenant from Ladder Company 27 in the Bronx. He has been a volunteer firefighter for more than 39 years. He is nationally recognized in the areas of emergency vehicle operations, apparatus placement, and apparatus purchasing.
J. GORDON ROUTLEY is the assistant director of the Montreal Fire Department in Quebec, Canada. He has been active in the fire service for 54 years in both Canada and the United States in a variety of career and volunteer roles. He is also a licensed professional engineer and a fellow of the Society of Fire Protection Engineers and the Institution of Fire Engineers.
