HEPA filtered cabs on heavy equipment

[David.Allen%EM@em.doe.gov]

      Does anyone out there have experience (successful or not) with
      using HEPA filtration on the cab of a bulldozer or backhoe or
      what-have-you (whether air-pressurized or not) to keep the
      operator out of a respirator, even when the area through which
      he may be driving would otherwise require one?

      Thank you.