Solution Summary: Dozers with Cab Filtration System
Operating heavy equipment generates a large amount of dust that may contain crystalline silica and other respirable contaminants, creating a hazard for the operator. Pieces of heavy equipment that can filter and pressurize the cabin air have been shown to effectively reduce operator exposure to dust and silica and should be considered as a dust control option. These systems use a cyclonic, or inertial, separator followed by one or more filters to remove particles from the air supplied to the equipment cab. Some systems may feature a second filter that cleans the cabin air that is recirculated. The filtration efficiency and protection provided by a system depends on the integrity of the cabin and the filtration system as well as filter efficiency.
NIOSH recommends a two or three filter system which includes a intake, a recirculation, and a final filter design. A powered intake filter system is also highly recommended which uses either a self-cleaning method such as a reverse pulse or back-flushing technique, or a centrifugal design to spin off the oversized particles (Cecala et al. 2014).
Komatsu offers optional cab air-filtration systems that provide pre-cleaned, filtered air to the HVAC system for several of their crawler dozer model. These cabs are pressurized to minimize odors and dust. We are only using Komatsu as an example for this draft but there may be other heavy equipment manufacturers and models that offer these cab air-filtration features.
Komatsu D155AX-7 WH
- Operating weight: 91,515 pounds
- Horsepower: 354 @1950 rpm
- Blade Capacity: 26.8 - 33.2 yd3
Komatsu D275AX-5 WH
- Operating weight: 113,604 pounds
- Horsepower: 449 @2000 rpm
- Blade Capacity: 17.9 yd3
Komatsu D85EX-18 WH
- Operating weight: 67,645 pounds
- Horsepower: 264 @1900 rpm
- Blade Capacity: 934 yd3
Operating heavy equipment is a high dust activity that in the absence of controls would place operators at risk of lung disease, cancer, chronic obstructive pulmonary disease (COPD), lung scarring, silicosis, renal disease and autoimmune disorders, such as lupus and rheumatoid arthritis, with prolonged exposure. Silicosis is an incurable, sometimes fatal disease. Such disease is well documented in the Vermont granite quarries and stone cutting sheds, and in construction operations. OSHA has a Permissible Exposure Limit (PEL) for exposure to respirable crystalline silica of 50 micrograms per cubic meter of air (µg/m3) based on an 8-hour time weighted average. A study on older enclosed cabs used on drills and bulldozers can easily exceed the OSHA standard and other recommended silica concentration levels when the silica content of the rock exceeds 5% (Organicak and Page 1999).
How Risks are Reduced:
Cab filtration systems use inertial separators followed by filters to remove particulate, including silica, before they enter the equipment cabin. In addition, some systems are equipped with a second filter to clean the cabin air prior to recirculation, further reducing concentrations in the cab and operator exposure.
Using filtration and pressurization systems will reduce the concentration of particulate, including silica, in the cabin, but the extent that it reduces the small, respirable particles will vary. The extent of the reduction is dependent on the efficiency of the filters used, the integrity of the cabin, the use of a recirculation filter, the presence of dust or silica sources inside the cabin and the nature and amount of work. Although exposure is not reduced to zero, data from manufacturers and researchers indicate exposure to dust and respirable silica can be significantly reduced through the use of filtration and pressurization systems.
Good enclosed cab air filtration systems have been shown to significanlty reduce silica dust inside the cab by 94% (Cecala et al. 2004). Inside cab dust concentrations can be also be variable, depending on outside concentrations surrounding the cab. Also, reducing inside cab dust sources such as floor heaters can provided additional assistance in lowering dust concentrations (Cecala et al. 2005).
Effects on Productivity:
Cab filtration systems can have either positive or negative effects on productivity, but definitely improve the quality of the work by removing large amounts of airborne dust, which allows a cleaner environment for operators. Improved worker comfort is a result of reduced airborne dust which may in turn result in less fatigue for the worker and greater productivity. In some cases, particularly where work is intermittent, use of cab filtration systems should be adequate to reduce the need to wear a respirator, and the need for an employer respiratory protection program.
There are additional conditions and practices that can improve the performance of filtration and pressurization systems and reduce dust and silica concentrations in equipment cab:
- The enclosed cabin must be leak-tested and sealed.
- Door and window gaskets can be replaced and cracks and holes sealed to improve cabin integrity.
- Doors and windows should be kept closed at all times.
- Cab floors should be kept clean of dust and debris. Some studies indicate that the use of floor sweep compounds may help reduce airborne dust originating from cabin floors.
- The performance of electrostatic filters decreases after a few months. This type of filter should be replaced on a fixed schedule, not on one based on hours used.
- Radiator-type floor heaters with fans have been found to significantly increase airborne dust concentrations in the cab by stirring up dust from the floor and the operator’s clothes and boots. This type of heater should not be used; if there is no other option then they should be positioned near the top of the cab.
For more information, NIOSH has a mining publication on Reducing Hazardous Dust in Enclosed Operator Cabs During Construction.
Jean Christophe Le, MPH - CPWR The Center for Construction Research and Training
Bruce Lippy, PhD - CPWR The Center for Construction Research and Training
Andrew Cecala - Centers for Disease Control and Prevention