CODE OF PRACTICE FOR METAL SCAFFOLDING SAFETY

(b) Outside buildings:
46
CODE OF PRACTICE FOR METAL SCAFFOLDING SAFETY
(i) The height to the least base dimension ratio for
stationary towers outside buildings without special means
of anchoring should not be greater than 3.5.
(ii) Stationary towers outside are usually exposed and are
therefore subject to wind forces. Towers, even with a height
to the least base dimension ratio less than 3.5, are unstable in
locations exposed to high winds. For these circumstances, the
wind forces should be calculated and the tower restrained by
kentledge or guys to give a factor of safety against overturning
of 1.5 in any direction.
(iii) Besides, when the ground is soft, sole plates should be used
and the tower should be maintained in the centre of the sole
plate by the use of substantial nails or other means. When the
ground is sloping, the sole plates should be dug in flat.
5.2.5 Mobile metal towers
This is also one of the commonly used types of free-standing metal towers
in Hong Kong. They are fitted with castors at the bottom of the standards.
The castors should be of the swivel type and fixed to the standards of
the scaffold so that they cannot fall off if the leg is out of contact with the
ground (See Figure 4 for details). There are different requirements when
being used within and outside buildings:
(a) Within buildings:
The height to the least base dimension ratio should be limited to 3.5.
(b) Outside buildings:
(i) The height to the least base dimension ratio should not be
greater than 3. When in use in exposed situations, the scaffold
should be tied to the building it is serving.