Fire Department, Ladder Company, Pumpers

Steel vs. Aluminum Aerial Ladders

Issue 4 and Volume 17.

 (1) Heat sensor warning labels are still required for aluminum aerial ladders. The orange dot turns black at 350°F, the temperature at which aluminum starts to anneal and lose its strength.
(1) Heat sensor warning labels are still required for aluminum aerial ladders. The orange dot turns black at 350°F, the temperature at which aluminum starts to anneal and lose its strength. (Photos by author.)
 (2) Four heat sensor warning labels are required on each section of the ladder. These dots are the size of a fingernail and not easy to see at night or in smoke. It is essential that firefighters check these labels after every fire and during weekly maintenance checks.
(2) Four heat sensor warning labels are required on each section of the ladder. These dots are the size of a fingernail and not easy to see at night or in smoke. It is essential that firefighters check these labels after every fire and during weekly maintenance checks.
 (3) These access ports at the base of the fly sections are where the waxy paraffin-based compound, NWAC 120-4, is sprayed into the hollow-tube steel members of the ladder. It is a highly effective cavity corrosion inhibitor that provides long-term protection for both ferrous and nonferrous metals.
(3) These access ports at the base of the fly sections are where the waxy paraffin-based compound, NWAC 120-4, is sprayed into the hollow-tube steel members of the ladder. It is a highly effective cavity corrosion inhibitor that provides long-term protection for both ferrous and nonferrous metals.

After researching wood vs. aluminum fire service ground ladders, the next logical step was to compare steel vs. aluminum aerial ladders. That started another great debate! For as many fire service professionals there are who swear by steel aerial ladders, there are just as many who feel aluminum aerials are superior and definitely the way to go.

On the surface, the pros and cons may seem obvious. Steel is stronger, but it’s also heavier. Aluminum is lighter, so aerials can be built taller. Steel can withstand higher temperatures than aluminum, but aluminum doesn’t rust so in the long run it does better in harsh, inclement weather. And on and on it goes-for every pro opinion, there’s a rebuttal con opinion.

Bigger and taller are not always better, and stronger usually means heavier. However, many of these pros and cons are governed by factors that have nothing to do with fire apparatus. For example, bigger and taller aerial apparatus may not fit inside existing fire stations. Heavier fire apparatus may exceed weight limitations on bridges, viaducts, and overpasses. Heavy rigs increase the cost of street maintenance because they tear up road surfaces over a period of time. Running over curbs and sidewalks, which sometimes can’t be avoided, cracks their surfaces, shortening their expected service life span.

Aluminum Aerials

Pound for pound, aluminum is lighter than steel. Reduced weight equals more payload capacity for equipment and water. There is less wear and tear on engine transmissions, brakes, and tires. This contributes to reduced maintenance costs and extends the service life of the apparatus. Aluminum resists corrosion and will not rust like steel. Aluminum doesn’t need to be painted, saving thousands of dollars in repaints over the lifespan of the aerial ladder. Alumninum ladder rungs are typically extruded (grooved) for a permanent nonslip surface. Steel rungs have rubber covers, which can get nicked and may require periodic replacements. A lighter aerial may be able to handle the added weight of snow or ice accumulation better than a heavier steel aerial. Manufacturers claim aluminum remains cooler and transfers heat faster than steel does, and the swirl finish assists in reflecting heat away from the aerial.

In 1999, Jeff D. Aiken, P.E. wrote a white paper called, “Thermal Characteristics of E-One Extruded Aluminum Aerials.” At the time, he was the new products manager for E-ONE. Although it’s an “in-house” publication, there was some very interesting information about aluminum. Aiken states that when the strength of aluminum at elevated temperatures was the only thermal property considered, it would stand to reason that it was unsuitable for aerial ladders that would be used in firefighting operations. However, further investigation and tests showed it was just as suitable as steel in normal high-heat fireground environments. Aiken writes, “Thermal conductivity, reflectivity, absorptivity, and specific heat must also be taken into consideration. It is well known that aluminum has a lower strength than steel at elevated metal temperatures. But, it takes a much higher rate of heat input into aluminum to raise its temperature equally with an equivalent piece of steel.”

There’s a lot of impressive technical information within the white paper, but we still need to use common sense with firefighters. Aluminum has to be beefed up to equal the strength of steel, and that adds weight. And from our knowledge of building construction, we know that steel will withstand temperatures up to 1,000°F before it will start to lose its strength. Yet, the National Fire Protection Association (NFPA) still requires aluminum aerials to attach four heat sensor labels to each section of the ladder. Remember, those heat sensors turn black at 350°F. That’s the temperature that aluminum starts to anneal and lose its strength. Someone smarter than me has to explain, if aluminum aerial devices can remain cool, transfer heat, and reflect it away, as Aiken states, why are they still required to have heat sensors for such low temperatures? Are aerial devices vulnerable to the same temperatures as aluminum ground ladders?

Don’t get me wrong. I like aluminum aerials. Ladder 6 (my rig) is the only aluminum aerial ladder in the Seattle fleet of twelve. It’s a big ladder. With wider ladder sections and high hand rails, it provides a safer and more secure climbing experience. I prefer it to our steel aerials, which are narrower and have shorter hand rails. You really have to use caution while climbing that last steel fly section, especially when carrying equipment. However, Ladder 6 is not the lightest apparatus of the straight frame Seattle ladder trucks; in fact, it’s the second heaviest.

Ladder 6 has a running weight of 55,200 pounds. Ladder 8 is a steel aerial and is the heaviest straight frame we have, with a running weight of 69,300 pounds. Ladder 12 is a steel ladder with a running weight of 55,000 pounds. Ladder 3 is a steel aerial with a running weight of 53,300 pounds. Our reserve steel straight frame ladder has a running weight of 53,200 lbs.

I realize I’m not comparing identical apparatus; these are just ballpark figures. But the rigs are all 100-foot aerials, and sizes are pretty close. The equipment inventory is standardized for truck companies throughout the department. I’m just noting that the weight of our aluminum aerial ladder truck is not significantly lighter than the steel ones.

Steel Aerials

On a recent trip, I met Bryan Smeal, of Smeal Fire Apparatus. A family-owned business founded in 1964, Smeal only makes steel aerials. As we discussed fire trucks, I asked Smeal, “Why only steel?” He said, “Because it’s stronger-period. Smeal has never had a steel aerial ladder failure, and we’re very proud of that. Steel rungs are stronger and better for high anchor points when using the aerial for high-angle rescues. Aluminum tends to sway more in windy conditions. Firefighters are visual. Fire damage to aluminum aerials is not obvious. We use PPG Delfleet paint. If our ladders are exposed to high heat, you can see the paint blister. That’s a clear warning sign for firefighters, so it’s a good thing.”

Smeal acknowledged the inherent problem with steel aerials-rust. “While thorough paint jobs prevent oxidation on the exterior of the ladder, the challenge was dealing with rust from within. After years of repetitive exposure to the elements, steel aerials rust from the inside out. But, Smeal figured out how to fix that by spraying the inside of hollow tube steel members with a waxy compound called NWAC 120-4.” Smeal showed me these small access ports about the size of a nickel at the base of each side of the fly sections and the bed section of the aerial ladder. A special wand is inserted into the hollow channels of the ladder where this paraffin-based paint is applied. NWAC 120-4 is a highly effective cavity corrosion inhibitor that provides long-term protection for both ferrous and nonferrous metals.

An Unbiased Opinion

NFPA 1914, Standard for Testing Fire Department Aerial Devices (2002 ed.), recommends annual nondestructive tests for aerial ladders to be performed by third-party companies. With all the certification requirements and liability, it’s best for fire departments to contract these services out to private companies. I figured if anyone would see the shortcomings of steel or aluminum aerials, it would be a neutral party. So I contacted Fire One Water-Based Fire Protection Services, located in Drexel Hill, Pennsylvania. According to the techs at Fire One, with all the different manufacturers tested, there is no difference between steel and aluminum aerial ladders. In the testing process, they both perform well. Neither type tested has failed to date, and both types of ladders meet or exceed NFPA 1901, Standard for Automotive Apparatus, and NFPA 1914.

What does this mean to the firefighter? Well, for many of us, nothing. We have the apparatus that we have. We should, however, take the maintenance of aerial ladders seriously, because there’s a lot more riding on those rungs and rails besides a roof ladder, an ax, and a pike pole-you are! For the rest of the fire service, a poor economy has created stiff competition between apparatus manufacturers to put the best product out there. And that’s good. All you have to do is walk the aisles of the trade shows like the Fire Department Instructors Conference (FDIC) to see that the new fire apparatus are impressive rigs.

RAUL A. ANGULO, a veteran of the Seattle (WA) Fire Department and captain of Ladder Company 6, has more than 30 years in the fire service. He is a member of the Fire Apparatus & Emergency Equipment editorial advisory board. He lectures on fire service leadership, company officer development, and fireground strategy and accountability throughout the United States, Canada, and Mexico.

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