Enclosed cabs of heavy equipment such as excavators, bulldozers, cranes, and backhoes must be well-designed and function properly or operators could be exposed to harmful concentrations of respirable crystalline silica.

A recent study in the American Journal of Industrial Medicine found that 79% of 100,000 workers exposed to silica dust above the recommended exposure limit worked in the construction industry.

Workers exposed to even small amounts of silica dust can, over time, develop silicosis, lung cancer, chronic obstructive pulmonary disease, and other debilitating illnesses.

The National Institute of Occupational Safety and Health has over many years studied the performance of enclosed cabs for protecting agriculture, construction, and mining industry workers from a variety of air contaminants.

The research has shown that filter efficiency and using a recirculation filter were the most important factors for enclosed cabs, and that an effective filtration system should remove at least 95% of respirable aerosols, including dust, diesel particulates, and droplets.

Sealing the cab’s interior from the outside environment prevents wind-driven contaminants from entering and reduces air leakage around the filters, the research shows.

Design Recommendations

NIOSH also recommends these design considerations for enclosed cabs:

  • Use a separate intake pressurizer fan and a high-efficiency respirable dust filter to supply air to the enclosure
  • Seal the enclosed cab from the outside to effectively reduce contaminants and attain positive pressurization.
  • Ensure that the system is recirculating filtered air inside of the enclosure
  • Locate the cab filtration system intake as far away as possible from potential contaminant sources
  • Avoid locating heaters, fans, or HVAC discharge vents near the cab floor since this can dislodge dust
  • Incorporate remote operator control of processes within the enclosure to reduce the need to open the enclosure
  • Monitor the performance with a cab pressure instrument as a measurable loss in pressure over time can indicate significant problems, including a reduction in intake airflow or loss of enclosure integrity
  • Size and locate filters to allow for easy replacement and maintenance
  • Select interior materials that retain less dust and are easily cleaned to reduce dust generation inside the enclosure

Standard

OSHA used NIOSH research to develop its standard for protecting workers in enclosed cabs from silica exposure. 

To comply, enclosed cabs need to be properly designed by the manufacturer or retrofitted to include these features:

  • An intake air filter that is at least 95% efficient for particles in the 0.3-10.0 μm range (e.g., MERV-16)
  • Free from settled dust
  • Door seals with properly working closing mechanisms
  • Gaskets and seals that are in good condition and working properly
  • Positive pressure with continuous delivery of fresh air
  • Heating and cooling capabilities

Cutting Exposure

Well-designed enclosed cabs should provide a comfortable, safe, and healthy environment for operators while cutting exposure to outside airborne contaminants, including silica dust.

The problem for operators is that it may be difficult to determine if the cab complies with the OSHA standard.

OSHA, NIOSH, and the Center for Construction Research and Training met with a trade association representing manufacturers to discuss the problem.

The Center for Construction Research also conducted a survey of 437 safety and health trainers, then published a hazard alert informing workers and employers on the importance of protecting workers from silica dust when operating machinery from an enclosed cab.

Checklist

The alert recommends that cab equipment operators complete these tasks before beginning work:

  • Inspect system filters for damage or airflow bypass and notify a supervisor if filters need cleaning or replacement
  • Inspect the cab daily for holes, gaps, and cracks around doors, windows, joints, power line entries, and controls, using silicone caulk or rubber gaskets
  • Notify a supervisor if a door gasket or window seal needs to be replaced
  • Check the pressure gauge daily to ensure it works and monitor it throughout the shift to ensure positive air pressure is maintained in the cab and dusty air is kept out

For more information, contact CBIA’s Phillip Montgomery (860.244.1982).