Vibration and Noise Exposures in Forestry Work

The forest products industry is a powerful economic presence in the Pacific Northwest.  Approximately 20,000 logging industry workers are employed in the Pacific Northwest, including about 7,700 logging employees in Washington State in 1998. Although mechanical tree harvesting methods are increasingly common, many workers are still exposed to hand-arm vibration (HAV) and whole-body vibration (WBV) from hand tools and heavy equipment.  These exposures put logging workers at risk of developing vibration associated diseases, such as Raynaud's Phenomenon or vibration white finger disease (VWF), and permanent noise-induced hearing loss.  Researchers affiliated with the University of Washington’s Pacific Northwest Agricultural Safety and Health Center (PNASH) are studying occupational vibration and noise exposures among forest workers to assess the potential need for exposure control measures and to evaluate the relationship between equipment noise and vibration exposure levels.

Vibration exposure has been associated with negative health effects such as hand-arm vibration syndrome and degenerative spinal disorders, while high noise levels can produce permanent, irreversible noise-induced hearing loss. These conditions prevent workers from performing their normal job tasks and reduce quality of life.

Although many studies have assessed the health effects of vibration exposure, very few data are available on actual exposure levels in forest workers. 

Data Collection: Stage 1 (Spring 1999)
Field data were collected at two large Washington timber companies. Monitoring was done on workers in 6 trades, 5 types of operations, 12 types of equipment, and 19 job activities. Participating workers reported the timing and number of tasks and tools used during the monitored workshift via activity cards developed for this project. Comparisons between worker self-reporting and researcher observations indicated that workers can report their activities very accurately, potentially allowing for estimation of unmonitored workers' exposures based on reported activities.

A total of 166 HAV and WBV measurements and 43 full-shift noise measurements were made at 10 sites over 8 weeks in spring 1999. The tasks and tools associated with the highest exposure levels were notching stumps and chainsaws (HAV), spreading rock with a vehicle and bulldozers (WBV), and unbelling chokers on landings and cable yarders (noise). The trades with the highest exposure levels were landing man (HAV), hooktender (WBV), and tree feller (noise). The operations with the highest exposure levels were yarding and landing (HAV and WBV) and tree felling (noise). Chainsaws and every type of heavy equipment measured exceeded recommended vibration exposure guidelines, while 60% of all noise exposures exceeded the WA State limit. No correlation was found between equipment noise and vibration levels.

Click here to view a manuscript summarizing the noise and vibration exposure findings of the 1st stage of data collection.

Date Collection: Stage 2 (Fall 2001-present)

The field sampling and data collection effort was expanded to include small contract loggers located in Washington, Idaho and Alaska. A total of 58 workers were assessed for noise and vibration exposure, health status, and work history in Northwest logging sites: 32 in Washington, 10 in Alaska, and 16 in Idaho.   Twelve office worker control subjects were recruited from the UW School of Public Health and Community Medicine, and silviculturist and forester control population sources were identified.  Control recruitment is ongoing.

Full-shift noise exposure measurements were made on 57 employees; 26 (46%) were overexposed by the relevant noise exposure regulation. All but one of the overexposed workers was observed using hearing protection. Every participating company reported having a hearing conservation program (HCP); however, HCP effectiveness was not evaluated. The highest noise sources were chainsaws, road graders, and front end loaders.  Two-hundred fifty-nine hand-arm and 115 whole-body vibration exposure measurements (374 total) on 49 workers. Fifty-seven percent of hand arm and 75% of whole body measurements were over the recommended 8-hour limits. The highest hand-arm vibration sources were chainsaws and front end loaders. The highest whole-body vibration sources were shovels and forwarders.

Click here to view a report summarizing the noise and vibration exposure findings of the 2nd stage of data collection.

For more information regarding this study, please call the PNASH Center at 1-800-330-0827, or visit their