Just as the sailor keeps a “weather eye” on the wind, so must the MEWP operator and workforce. As part of the pre-work risk assessment it is important not to forget the possible effects of a change in wind speed. This is particularly so for those offering tree work.
A powered Spiderlift access platform that works outside will operate up to a maximum wind speed that will have a mark on the machine or available in the hand manual. Operation above the maximum wind speed could cause instability and affect the safety of both operator and those below. As a guide, wind speeds above 28mph pose a safety risk making it uncomfortable and dangerous for the operator to continue to work.
Other wind factors may also increase the risk of accidents during tree work. Wind chill has a serious impact on the ability to work safely at height. On a cool calm day with a temperature of 10 degrees C, it may feel comfortable enough. However, when the wind rises to 20mph the effect on the hands and face is to lower it to 0 degrees! If work was to begin at 0 degrees C on the ground and the wind become to rise to 20mph, then the effect on the skin comes -15 degrees C. Obviously it is important to wear very warm clothing at such temperatures.
It should always be remembered that wind speed increases with height. At 20 metres above ground it could increase by 50%. The recommendation is that operators carry with them a hand held anemometer that they can quickly check at platform level. This essential piece of arborist equipment is available for less than £10 and measures wind speed, wind gust, wind chill and temperature. The anemometer comes with a lanyard for all powered access platform operators.
This wind force scale was devised at the beginning of the 19th century. It is still useful today as it is based on visual and subjective observation. The normal scale ranges from zero to 10. Working at height on at the scale of zero to 5 is considered safe. However at Level 6 – Strong Breeze – opertaters will be more cautious. Wind speed at this level ranges from 25 to 31 mph. The “safe” speed of 28 mph can easily move into a dangerous situation. All tree work at levels above Level 6 is completely unsafe.
Always include wind speed in the pre-start risk assessment and monitor throughout the progress of the tree service when using forestry access platforms. The hand held anemometer is a cheap practical tool for tree work when operating in the raised basket. A quick check will reduce the risk of instability and highlight freezing “wind chill” conditions.