Evaluation of Different Diesel Exhaust Control Methods at Three Fire Stations

1724 

Professional Poster 

H Echt¹

¹N/A, Cincinnati, OH

Hannah Echt  
N/A

The NIOSH HHE Program evaluates health and safety concerns in various workplaces throughout the United States in response to requests from employees, unions, and employers. Three municipal fire departments, each with different diesel exhaust control methods, requested an HHE to compare how effective each method was in controlling diesel exhaust emissions in fire stations.

Fire departments use a variety of different strategies to control diesel exhaust emissions in fire stations. These include exhaust filtration systems, tailpipe exhaust ventilation, and dilution ventilation. The HHE Program received a request from three fire departments to evaluate and compare these control methods at three fire stations. One station was equipped with an air filtration system consisting of ceiling-mounted units in the apparatus bay. Another station's apparatus bay was equipped with a local exhaust extraction system consisting of ceiling-mounted exhaust hoses which connected to the vehicle tailpipes. At the third station, most of the diesel-powered apparatuses were equipped with ceramic diesel particulate filters in the vehicle's exhaust system. In addition to these control methods, each station had general exhaust systems in their apparatus bays.

"We did the following activities during our two-day visits at each station:
We observed work processes and practices and collected information on the number of runs made, work processes, and workplace conditions.
We collected area air samples of diesel particulate (as elemental carbon) during one 12-hour and one 8-hour period in the apparatus bays living quarters (e.g., kitchens, dormitories); report rooms; and outside the fire stations (as a reference sample). We collected the air samples at a flow rate of 2 L/min on a three-piece, 37-mm open-faced cassette with a health-treated quartz-fiber filter. We analyzed each sample for elemental carbon using NIOSH Method 5040, using thermal optical analysis.
We measured near real-time concentrations of particulates, carbon monoxide, and carbon dioxide over a 32-hour period in the same sampling locations as the area air samples for diesel particulate. We used TSI DustTrak DRX 8533 aerosol monitors to log particle mass concentrations every 30 seconds in different size groups: PM1, PM2.5, respirable PM, PM10, and total PM. We also used TSI Model 3007 handheld condensation particle counters (CPCs) to log particle number concentrations every second in the size range of 0.01to > 1 µm. We used TSI Q-Trak indoor air quality monitors to measure carbon monoxide and carbon dioxide concentrations every 30 seconds.
We conducted ventilation assessments at each station. We used a TSI Velocicalc with an attached rotating vane anemometer to take measurements for the general exhaust ventilation systems serving the apparatus bays. Velocity readings were taken across the face of the discharge outlet for exhaust fans, supply air diffusers, and exhaust grilles. A micromanometer was used to measure differential pressure across the doorways separating the apparatus bays from the living quarters. To supplement the quantitative pressure readings, smoke tracer tests were conducted at each doorway to observe airflow direction and confirm pressurization relationships.
Airflow from the ceiling-mounted industrial air cleaners was measured by removing the downstream access cover and positioning a TSI Alnor flow hood with a 2 ft x 2 ft skirt directly over the unit outlet. This setup allowed for direct volumetric airflow readings to be obtained at the discharge of the air cleaner. Particulate filtration efficiency was estimated by measuring upstream and downstream particle counts with a CPC.
Ventilation measurements for the local exhaust extraction system were taken using a TSI Velocicalc with an attached rotating vane anemometer. Velocity readings were taken at the vehicle exhaust capture hose inlet while it was disconnected from the tailpipe, and the measured average velocity was multiplied by the free area of the opening to calculate volumetric airflow. Total exhaust flow for the local exhaust extraction system was also measured at the fan discharge outlet located on the roof. Velocity readings were also taken at the tailp

"Area air concentrations of carbon monoxide, carbon dioxide, and particulates were well below occupational exposure limits. Elemental carbon was not detected in any of the area air samples. While these were not personal samples, the samples were collected near where employees typically worked. Most of the particles were less than 1 µm in diameter. In general, average particle concentrations were higher in the apparatus bays while diesel engines were running compared with the other sampling locations.
Measurement of upstream and downstream particle counts at the air filtration unit showed an 87% reduction in particle concentrations (in the size range of 0.01 to > 1 µm) as air passed through the filters. Although the air cleaners were programmed to operate for approximately 9-10 minutes after activation, particle concentration data indicated that it sometimes required approximately two hours for the particle concentration to return to background levels. This suggests that the air cleaners were insufficient to adequately reduce the diesel exhaust burden in the apparatus bay. Increasing the air cleaners' operating time could improve ventilation in the bay but implementing source control may be more effective.
Multiple operating issues were observed for the local exhaust extraction system. The fire engine's tailpipe (a double-walled sleeve) did not fit onto the local exhaust extraction system's hose, leading to a decrease in backpressure and a large portion of the engine exhaust not being captured by the local exhaust extraction. Furthermore, the system was only activated by dispatch calls. Only one fire truck had exhaust that created enough air pressure to activate the local exhaust extraction system without a dispatch call. We also observed that firefighters needed to manually connect the local exhaust extraction hose to the vehicle's tailpipe when the vehicle returned and the engine was on. As a result, firefighters may experience peak (short-term) exposures to diesel exhaust when reattaching the hose to the running vehicle. Evaluating whether the pressure activation threshold for the local exhaust system can be adjusted to improve sensitivity and reliability could help decrease diesel exhaust concentrations. The addition of engine-start detection or engine-running sensors as supplemental activation methods would ensure the system engages reliably in concert with the existing pressure and dispatch call triggers.
Particle concentrations (in the size range of 0.01 to > 1 µm) were between 10 to 15 times higher in vehicles that did not have engine exhaust filters than in vehicles with filters. We also observed that particle concentrations were higher for filter regeneration compared with routine engine starts. We observed consistent peaks in particle concentrations in the apparatus bay during engine start events, but these levels returned to background within a few minutes and remained substantially lower than levels in the apparatus bays at the

Engineering Controls and Ventilation

Exposure Assessment