Close Call: Wind event topples trees

Location: 
Babine Lake Road (near Smithers, BC)
Date of Incident / Close Call: 
2011-07-08
Company Name: 
Windfirm Resources Inc.
Details of Incident / Close Call: 

While tree planting crews were working on a BC Timber Sales tree planting project, an early morning breeze increased significantly by mid-morning. At around 10:30 a.m. two different crew leaders reported by radio that they had seen a tree toppled by the wind on their block. The site supervisor immediately radioed all crews to initiate an emergency evacuation. Within a half-hour, every crew member was safely accounted for back at the trucks and the crew returned to camp for the remainder of the day.

A debrief with the crew leaders and site supervisor focused on the fact that due to a very wet spring the water table is quite high on many of the blocks. This makes live trees very susceptible to being blown over, especially large cottonwoods which have been left standing throughout the blocks. In this event, the wind was estimated to be gusting from 35 to 45 kilometres per hour.

Learnings and Suggestions: 

Silviculture or other workers should be familiar with easy field methods to estimate wind speed and have pre-determined thresholds to initiate evacuation. In this case, the crew leaders and site supervisor used a Beaufort Scale wind chart on their block checklists that helped to identify the level of wind disturbance and provided guidelines for appropriate guidelines actions to take at different wind levels.

The Beaufort Scale indicated that the breeze was gusting from 40 to 50 kms/hr, which is a Level 6 on the Beaufort Scale. The recommended action at this level was to avoid the tree line or residual patches, and initiate an immediate evacuation to the vehicles until the wind returned to a safe level.

The crew leaders were also instructed to check for weakened or fallen trees that might be hazardous before they returned to work the next day. In one case, a 24-inch diameter cottonwood had to be cut, as it had fallen directly across the main quad road in the block.

For more information on this submitted alert: 

Rick Ness, Windfirm Resources Inc. 250-847-1063 rick@windfirm.ca

File attachments
Wind_event_topples_trees.pdf
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