Test for the Integrity of Environmental Tractor Cab Filtration Systems

Abstract

Cab filtration systems can be used to protect vehicle operators from hazardous air contaminants. In a cab filtration system, a fan draws air through filters and pressurizes the cab with this filtered air. This article describes the application of a low-cost, optical particle counter to evaluate the performance of tractor cab filtration systems. The tractors were equipped with environmental enclosures to protect the operators from pesticide exposures that occur during air blast spraying in orchards. Prior to testing, all environmental tractor cabs underwent a complete maintenance overhaul followed by a careful inspection by the manufacturer's field representative. As part of this maintenance effort, 13 tractors with cab filtration systems were tested in an enclosure. A Met One model 227B two-channel optical particle counter was used to measure the aerosol concentration outside and inside the cab. Ambient aerosol and/or aerosol generated by burning incense sticks were used to challenge the stationary cab filtration system in an enclosure. The ratio of the outside to inside concentration (Co/Ci) is the exposure reduction attained by the cab system. Alternatively, the inside concentration divided by the outside concentration times 100 (Ci/Co x 100) gives the percent penetration. All 13 tractors were tested for leak sites. Leak sites were identified and sealed. This process was repeated until each cab showed an exposure reduction ratio Co/Ci of at least 50 (aerosol penetration into the cab Ci/Co x 100 was less than 2%) at the 0.3-0.5 microm particle size interval.

Field Assessment of Enclosed Cab Filtration System Performance Using Particle Counting Measurements

“…Other studies have measured notable internal particulate generation from blower motors (200 to 1,800 Particles/L) and have used incense smoke generated around a vehicle cab tested inside a temporary constructed field enclosure when outside cab concentrations were less than 42,000 Particles/L to make this error insignificant. (3,5) The minimum outside particle count concentrations needed for cab testing is currently open to discussion, but the laboratory test results discussed here indicate that the minimum may be somewhere around 20,000 Counts/L. However, internal cab particulate generation and instrument coincidence errors both tend to err conservatively with respect to cab protection factor measurements.…”

“…(3) Alternative particle counting cab field test procedures have been examined by NIOSH with submicron particles (0.3-0.5 μm) and have been used to quantify and improve agricultural tractor cab protection performance for pesticide spray applications. (4,5) One procedure used two optical particle counters alternated between the inside and outside locations of the tractor cab during four mobile test replicates, similar to the ASAE consensus standard test except that 0.3-0.4 μm particle sizes were used as the test medium. This field study identified and sealed several tractor cab filtration system leaks around a high-efficiency particulate air (HEPA) filter, which effectively reduced particle penetration into the cab from 11% to less than 1%.…”

“…This procedure was used to quantify cab protection factors of at least 50:1 (outside to inside particle concentrations) for a pesticide spraying company after refurbishing and performing maintenance on 13 tractor cabs. (5) Particle counting measurements of submicron (0.3-1.0 μm) particulates in ambient air were further used by NIOSH during laboratory experiments with multiple instruments to study the key design factors of enclosed cab dust filtration systems. (6) During these experiments two particle counting instruments were alternated between test replicates to average out any measurement biases between instruments, similar to the ASAE procedure described above.…”

Design, testing, and modeling of environmental enclosures for controlling worker exposure to airborne contaminants.

“…Alternative particle counting cab field test procedures have been examined and used by NIOSH with submicron particles (0.3-μm to 0.5-μm) to quantify and improve agricultural tractor cab protection performance for pesticide spray applications [Heitbrink et al 2003;Moyer et al 2005]. One procedure used two optical particle counters alternated between the inside and outside locations of the tractor cab during four 30-min tests, similar to the ASAE consensus standard test, except that 0.3-μm to 0.4-μm particle sizes were used as the test medium.…”

“…In this procedure, a two-channel particle counting instrument sampled alternate positions inside and outside an unoccupied cab using equal lengths of sample hoses to these locations. This procedure was used to quantify cab PFs of at least 50:1 (outside to inside particle concentrations) for a pesticide spraying company after refurbishing and performing maintenance on 13 tractor cabs [Moyer et al 2005].…”