Permanent platform
The placement of the work platform shall be between 500 and 900 mm under the upper edge (crown) of the chimney. Deeper chimneys (where one needs to stretch to reach the duct) must have more highly-positioned working platforms, about 500 mm under the chimney crown. For smaller chimneys, for example chimney flues, the work platform should be further down, about 900 mm under the chimney crown.