In August 1988 the Centers for Disease Control and Prevention, in Current Intelligence Bulletin 50, Carcinogenic Effects of Exposure to Diesel Exhaust, described the workplace hazard presented by diesel engine emissions. It said that studies on animals confirmed the potential carcinogenicity of whole diesel exhaust and that the exhaust should be regarded as a potential occupational carcinogen.
In the 24 years since that publication was issued, the body of knowledge linking diesel engine emissions to cancer and respiratory illnesses, such as asthma, has continued to grow. We also have a better understanding of the ingestion and absorption hazards that exist when the particulates and gases from diesel engine emissions are allowed to exist within our fire stations.
The dangers are real and the exposures more than passing. Even with the doors open, it doesn't take long to catch whiff of diesel exhaust when the apparatus is running in the bay.
Today's vehicle exhaust removal systems are a critical component in maintaining a fire station atmosphere that is free of the particulates and gases present in diesel engine emissions.
There are three basic types of systems that meet emission-reduction goals set forth in the applicable laws, regulations and standards: direct-source capture using hoses; direct-source capture using filtration; and filtration systems for building spaces. Some of those applicable laws, regulations and standards are Environmental Protection Agency 2007 Highway Diesel Rule (EPA07); NFPA 1500 (Section 9); OSHA; the International Code Council (Building Code); and United States Fire Administration's Assistance to Firefighters Grant Program Guidelines.
Direct-source capture system (hose-based)
This system uses the increasingly familiar orange or yellow flexible hose, which attaches directly to the apparatus exhaust pipe to capture the engine emissions before they can leave the vehicle's exhaust system.
Manufacturers use either a pneumatic boot or a magnetic coupling attachment to connect the hose to the exhaust pipe. The contained emissions are routed out of the building using exhaust fans and ductwork.
These systems rely on timers to control their functions. The system is activated when the vehicle is started and will continue to run for a pre-set time; the end time is usually set to allow enough time for a crew to mount the apparatus and the apparatus to safely exit the building.
The emission exhaust hose follows the exiting vehicle along a track until the vehicle reaches a pre-determined threshold, at which point the exhaust hose disengages from the vehicle's exhaust pipe and retracts back to its original position.
In addition, these types of direct-source capture systems can include the following specialized equipment to fit the various needs and layouts of fire stations:
- Track systems for single-lane, back-in bays.
- Rail systems for drive through bays or bays where vehicles are parked in tandem.
- Vertical stack systems for vehicles with overhead exhaust stacks.
The advantages of these systems is that diesel engine emissions are captured before they enter the station. The technology is time-tested. And the hoses and equipment provide visual reminder to station personnel to hazards of diesel engine emissions.
The disadvantages to these systems include replacement costs for hoses and retracting gear that become damaged. They also require that station personnel have competency using the system and comply with operating procedures. And they don't allow for moving apparatus around within station.
Direct-source capture system (vehicle-mounted filtration)
This second type of direct-capture system consists of a specialized filter and diverter that are mechanically installed alongside the vehicle's exhaust system. The system uses an electronic control device that automatically diverts the vehicle's exhaust flow from its normal path and through the filter after the vehicle starts.
This cycle time can be adjusted — anywhere between 10 and 99 seconds — to allow sufficient time for the vehicle to safely leave the station. Once the set time has elapsed, the diverter reroutes the exhaust stream from the filter and back to its normal route through the muffler and out the exhaust pipe.
The system also engages when the vehicle is placed in reverse, say for backing into the fire station. After the vehicle has been backed up and shifted out of reverse gear, the system will continue in the filter mode for the pre-set time to ensure that no unfiltered emissions enter the station.
One advantage is that these systems capture engine emissions before they enter station. And the system automatically engages without human intervention. There is also no equipment hanging from ceiling to apparatus floor, and apparatus can move anywhere in station and system still functions.
Initial costs for installation on the apparatus is one of its drawbacks. The cost of filter replacement also can be a problem.
Building space filtration systems
These systems exchange the air in the apparatus bays by pulling particulates and gases through a series of filters. Filtration systems are typically mounted to the ceiling and diesel emissions are forced through a series of disposable filters that trap particulates and chemically absorb other exhaust components.
Some manufacturers offer filtration units that have a fourth-stage photo-catalytic oxidizer that is said to kill airborne viruses and bacteria. This is not a bad option considering how much EMS work many departments do.
Door switches or electric eyes that detect vehicle movement serve as system activators. Once activated, the typical filtration system runs for a user-determined period, usually 15 to 20 minutes, to exchange the air several times.
These filtration units have air-flow rates of 3,000 to 6,000 cubic feet per minute. The number of units required for a particular space is determined by the size of the space to be filtered and the number of times the air in that space needs to be exchanged to achieve proper air filtration.
These systems involve the least amount of work necessary to install as only an electrical power source and ceiling mounting space are needed. Another advantage is that no vehicle modifications are needed.
System automatically engages without need for human intervention. It also filters air for other hazards besides diesel engine emissions, such as exhaust from small engines for hydraulic rescue tool being used to teach a class on vehicle extrication in the apparatus bay. And, apparatus can move freely around apparatus bay.
However, the initial cost and that of replacement filters, depending upon the number of units that may be required, may be great. Also, engine emissions, especially particulates, initially enter the space and can land on hard surfaces, making their removal by the filtration system difficult.