Anthropometric study answers firefighter size questions

By Gordon Routley

How big is a firefighter? Although that sounds like a fairly simple and straightforward question, the answer turns out to be very complicated and leads to many more questions. The United States fire service is now in the process of being examined, measured, and documented in a manner that goes far beyond all previous attempts.

The scientific field of anthropometrics (literally “human measurement”) is concerned with the physical sizes and shapes of humans. The development of an anthropometric data base for firefighters will provide much more information than has ever been available in the past to ensure that our tools, equipment and clothing are designed to fit the users and accommodate our wide range of sizes and shapes.

Protective clothing manufacturers have gradually developed an expanded range of size options based on the need to fit an increasing variety of firefighter bodies, although many individuals, particularly females and smaller males, still complain about the inadequate range of standard sizes. Clothing has evolved primarily through trial and error or “made to measure” processes.

Until very recently, most of the size and shape factors that were used by fire apparatus and equipment designers were based on some very basic and outdated assumptions about the weights and dimensions of firefighters. Much more comprehensive data is now available and even more will be produced in the next few years. All of this came from a determined attempt to study an important safety issue and the initial results have immediate implications for the design of fire apparatus.

The Seat belt Problem

In the spring of 2005, an informal task force was assembled to focus on the fairly basic problem of ensuring that the seats and seat belts in fire apparatus would accommodate the range of firefighters who are expected to use them. The ongoing effort to ensure that every firefighter will be properly seated and secured in an approved riding position brought attention to a problem that had been ignored or glossed-over for at least a decade: firefighters were complaining that they simply could not fit into the seating areas and fasten the seat belts in their fire apparatus. This news came as a surprise to many individuals who assumed that the dimensional requirements specified in National Fire Protection Association (NFPA) Standard 1901, Standard for Motor Fire Apparatus, ensured that vehicles could accommodate almost any firefighter.

The first meeting was organized as a joint effort of the National Fallen Firefighters Foundation and the Safety Health and Survival Section of the International Association of Fire Chiefs and brought together members of the Safety Task Force of the NFPA 1901 Committee, apparatus manufacturers, seat manufacturers, seat belt manufacturers and several interested fire service members, along with some experts in the study of anthropometrics. One of the facts that was revealed at the first meeting was that the standard dimensions that are incorporated in the NFPA Standard for Fire Apparatus came from sources and assumptions that had been developed decades ago and for very different purposes.

Those standard measurements for seats were based on providing sufficient space for the 95th percentile firefighter; incorporating the assumption that the space might not be sufficient for one firefighter in twenty. The 5 percent factor was a commonly accepted design standard, based on the expectation that some people are just “too big” or “too small”. Before the study of anthropometrics became sophisticated, most designers would aim to accommodate a range of individuals from the 5th percentile female at the small end to the 95th percentile male at the large end, anticipating that about 10 percent of the overall population would be outside the standard size range.

Experts in the field of anthropometrics have determined that the concept of a 95th percentile individual is highly theoretical. Humans come in a tremendous range of shapes and sizes with an infinite potential for variations in the relative dimensions of their body parts. A study conducted by an office chair manufacturer concluded that an adjustable chair designed to accommodate a range from the 5th percentile female to a 95th percentile male would really meet the needs of less than 68 percent of the overall population.

An individual who meets the accepted definition for 95th percentile in height would be slightly over 6’3″ tall, but that individual could have long legs, a short torso and no neck or short legs, a long torso and a long neck. A fire apparatus cab that provides enough headroom above every seat for a theoretical 6’3″ firefighter does not necessarily fit every firefighter who is less than 6’4″ in overall height. And where does the 6’5″ firefighter sit? And what about the vertically disadvantaged people at the other end of the scale?

Height is only one relatively simple consideration when we look at the problem of designing fire apparatus (as well as tools, equipment, and clothing) to fit the users. The data that has been used to define minimum standard fire apparatus dimensions came from a study of military personnel that was conducted half a century ago. The height, weight and overall dimensions of the general population have been increasing steadily for generations, so a set of measurements for the 95th percentile soldier from 50 years ago is undersized in relation to our 21st Century population. We also tend to attract a relatively high percentage of “bigger than average” individuals into the fire service, so our larger firefighters are even larger than the average large person. At the same time diversity has brought more individuals with smaller dimensions and non-standard shapes into the fire service–and we expect them to sit in the same seats.

The size issue is expanded when we dress our firefighters in bulky protective clothing that makes them even bigger, stuff the pockets and attach additional paraphernalia on the outside. The reports that many firefighters couldn’t squeeze themselves into the spaces provided for them and fasten their seat belts began to make sense as the information was analyzed. Detailed analysis was urgently needed to address the issue of seats and seat belts and the overall scope of the problem turned out to be much broader. It was a case of the closer you look – the more problems you discover.

Laser Scanning Study

The discussions that occurred in 2005 and 2006 resulted in the first scientific study to use modern technology to gather accurate anthropometric data from a representative group of firefighters. In essence the project applied 3-dimensional laser scanning to determine the body surface dimensions that should be used to ensure that fire apparatus fits today’s firefighters wearing their protective clothing and equipment. The laser scanner that was used to measure the firefighters, with and without their protective ensembles, was previously used for a similar project; to ensure that the cockpits of US Air Force planes are properly sized for their pilots.

The project was sponsored by the National Fallen Firefighters Foundation and conducted by Total Contact Inc, a technology firm that specializes in full body laser scanning. A representative sample of firefighters was obtained by working with several fire departments across the United States and ensuring that a statistically validated sample of male, female, Caucasian, African-American, Hispanic, Oriental and Native American were included.

The data produced by the project is now available from the National Fallen Firefighters Foundation and will have very significant applications in many different areas, reaching far beyond cab and seating dimensions. The same data can be applied to any item of protective clothing, equipment, tools and apparatus that should be designed to fit real firefighters.

Seat Dimensions

The first application of the data produced by this study should influence the dimensions of seating areas in fire apparatus cabs. The NFPA standard currently requires a minimum of 18 inches of width at the seat level and 22 inches at shoulder level. These dimensions allow for a seat to be squeezed into a space that barely accommodates an 18-inch wide seat cushion between the engine enclosure and a cab wall or door. The shoulder level generally provides the full required 22 inches, although the individual may have to lean a little to take full advantage of the space.

Click to enlarge

Click to enlarge

1-2. The scanner produces data files that allow every anthropometric dimension to be analyzed and compared for a wide range of body shapes and sizes, as well as different protective clothing ensembles. The results will be useful for a wide range of purposes, including fine-tuning size and shape variables for protective clothing and equipment.

The first stage of the NFFF anthropometric study confirmed exactly what many firefighters had already determined through unscientific trial and error–they couldn’t squeeze themselves into their seats and then fasten their seat belts around them. The data indicates that the minimum width should be increased by at least four to six inches to accommodate a firefighter wearing protective clothing. (The 2008 edition of NFPA 1901 requires longer seat belts to fit around the girth of larger bodies, although the seating areas dimensions have not been addressed.)

Click to enlarge

Click to enlarge

3-4. The three-dimensional laser scanner maps every detail of the surface of each subject in seated and standing positions. Each scan is conducted with and without protective clothing in order to fully appreciate the dimensions that must be accommodated for different situations.

The 22-inch allowance for shoulder width allows up to four seats to be placed in a row across the inside of many cabs. Although it is convenient to squeeze as many firefighters as possible into a cab, especially for volunteer departments, this often results in firefighters riding side-saddle and tangling SCBA straps and elbows as they try to figure out how to fasten their seat belts. This problem is even more severe when twin banks of four seats are placed face-to face with no allowance for 16 boots and 16 knees in the narrow aisle. Increasing the seat spacing requirement would limit most cabs to three seats per row, which might reduce the number of crew members, but ensure that all could ride safely.

The data that was produced by this initial study has many more applications, extending far beyond seat widths and seat belt lengths. The data should be valuable to every organization that makes things that have to fit firefighters.

The NFFF-sponsored project generated serious interest at the National Institute of Occupational Safety and Health (NIOSH). NIOSH is planning to conduct a much larger and comprehensive 3-year study of firefighter anthropometrics and ergonomics beginning in 2009. Previous NIOSH studies have applied the same technology to high risk occupational groups, including truck drivers and farmers. Firefighters will be the next occupational group to benefit from this important safety research.

J. Gordon Routley served as fire chief in Shreveport, Louisiana; Assistant to the Fire Chief in Phoenix, Arizona; and Safety Officer in Prince George’s County, Maryland. He is currently the Technical Advisor to the fire chief in Montreal, Canada, and provides consulting services to fire departments and fire service-related organizations in the United States and Canada, with an emphasis on firefighter health and safety. He is also the liaison representative for National Fallen Firefighters Foundation on the Board of Directors of the IAFC Safety, Health and Survival Section.

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