How to quiet older fire apparatus

Exposure to the noise pollution from diesel engines on fire apparatus presents a significant risk to firefighters’ hearing. Whether driving or riding aboard the apparatus, this is part of a firefighter’s work environment.

Another part of that work environment is working around operating diesel-powered fire apparatus, particularly for the driver/operator. In this context, firefighters have an even higher potential for auditory insult from noise because any noise shielding provided by the crew compartment is no longer present.

Exposure to noises of 80 decibels (dB) or greater for more than 15 minutes per day can cause long-term hearing loss. What does that sound like?

• Jet engine at take-off or a gunshot is more than 140 dB.
• Amplified concert music or an emergency siren is 120 dB.
• Motorcycle, chainsaw or MP3 player (at full volume) is 110 dB.
• A vacuum cleaner or alarm clock register 70 dB.

While the use of hearing protection, like noise reducing earplugs or earmuffs, should be a standard operating practice for personnel working around operating fire apparatus, it is also incumbent upon fire department leaders to seek engineering remedies for the apparatus itself.

This is particularly true for older fire apparatus that may still be in first-line or reserve operating status; older fire apparatus likely lack the engine noise-reduction features of newer fire apparatus.

According to the Centers for Disease Control and Prevention, there are eight components of a successful hearing loss-prevention program.

1. Noise exposure monitoring.
2. Engineering and administrative controls.
3. Audiometric evaluation.
4. Use of hearing protection devices.
5. Education and motivation.
6. Record keeping.
7. Program evaluation.
8. Program audit.

NFPA 1911: Standard for Automotive Fire Apparatus contains some specific requirements for noise reduction when upgrading or refurbishing existing fire apparatus in accordance with NFPA 1912: Standard for Fire Apparatus Refurbishing. In Appendix D.3, you’ll find:

• Noise levels in the driving and crew compartment(s) meet the current standard or appropriate hearing protection is provided (D.3, Item 9).
• All horns and sirens are relocated to a position as low and as far forward as possible. (D.3, Item 10).

Check the basics first

Kevin Last, owner of Vancouver Axle and Frame, where they work on lots of heavy trucks, says increased noise in older fire apparatus can likely be attributed to faulty or loose engine mounts.

“Replace those mounts if they’re bad, or tighten them up, and you’re going to see a big improvement,” Last said.

He added that another source of excess noise may be in the truck’s exhaust system. “Newer exhaust systems, particularly the muffler, are also designed and manufactured for greater noise reduction.”

Over the past few decades, there have been several laboratory tests on diesel engines in heavy trucks looking for ways to reduce engine noise inside the operator compartment. The body of knowledge gained from those studies have proven that noise emission can be reduced by more than 10 dB by applying insulation directly to the truck cab or by totally enclosing the engine compartment with noise-dampening material.

In 1973, John Rönnhult published a technical paper, “Reducing Noise from Heavy Diesel Trucks by Engine Compartment Shielding” for the Society of Automotive Engineers describing how significant diesel engine noise could be reduced through soundly designed shielding, without the need for modifying the basic design of the truck.

For older fire apparatus that could be too loud (above OSHA specifications), there are products made of noise dampening material on the market from several manufacturers.

Voices of experience

Some of them are backed with aluminum bendable material as well as self-adhesive material. Many of these commercially available noise-dampening products are also designed to reduce the amount of heat transmitted from the engine compartment to the crew compartment.

One mechanic on the emergency vehicle technician forum board, EV Tech Talk, shared his experience with quieting an old rig.

“The one [noise dampening product] I used several years ago was about 1/8-inch thick and reflects heat as well,” he wrote. “I used some on a 1958 conventional cab Oshkosh truck used at our airport for runway maintenance as it was quite loud inside the metal cab. Everything echoed due to being completely surrounded by metal.

“I installed it along the firewall inside the cab and under the hood, coating the entire hood including both side panels. It lowered the noise in the cab by more than 20 decibels.”

Vid Sansanwal, vice president and CFO at Front Line Emergency Vehicles, took a different approach.

“A year ago, we lined the floor of an older apparatus with Dynamat and then covered over it with a rubber lining,” Sansanwal said. “Our client feels it lowered the interior noise level significantly.”

New rig noise

New fire apparatus and ambulances meet the more stringent EPA regulations on engine emissions – which include acceptable noise levels – that started back in the 1990s. Now, most cab noises come from added equipment and not from the engines themselves.

Siren speaker placement causing noise to reverberate back into the cab, headset intercom systems with the volume set too high, external radio speakers inside the cab too close to the personnel, and outside noise from the windows being down all play into increased noise exposure for personnel.

When specifying new fire apparatus, fire department leaders should ensure that noise reduction is properly addressed when developing those specifications. Greater use of noise dampening technology should be specified for the crew compartment as well as the engine compartment itself.

While commercially available noise dampening products can be installed after-market, it’s likely that the process would be much easier – and potentially cheaper – to have the installation done at the factory.

Why does the engine have to be close to the crew compartment at all?

“We recently delivered a rear-mounted engine apparatus to a client located 8 hours north of Toronto,” Sansanwal said. “My drivers, [who delivered the apparatus] and who are all full-time firefighters, praised how quiet the cab was. They were happy that they could have a conversation without need of headsets.”

That’s definitely something to ponder in the quiet moments when writing up the specifications for your next piece of fire apparatus.