Stability and Outriggers Flashcards

What is the danger of using a tower scaffold in an area with vehicle traffic?

Answer: Vehicles can collide with the tower causing immediate collapse, and traffic vibrations can loosen components

Vehicle impact is a leading cause of tower scaffold collapse. Even a low-speed collision can overturn a tower. Physical barriers (concrete blocks, parked vehicles between traffic and tower) must be used, and traffic management plans implemented.

What is 'racking' in relation to tower scaffold stability?

Answer: The lateral swaying or distortion of the tower frame from a rectangle into a parallelogram shape

Racking is when horizontal forces cause the tower's rectangular frame to distort into a parallelogram shape. This is resisted by diagonal braces, which triangulate the structure. Without adequate diagonal bracing, racking can lead to tower collapse.

Why is it important that all four castors of a tower scaffold are on the same level plane?

Answer: If they are not level, the tower leans, shifting the centre of gravity and reducing the effective base size on one side

If all four castors are not on the same level, the tower leans, reducing the restoring moment on the lower side. In extreme cases, one castor may lift off the ground, effectively reducing the base to a triangle and dramatically reducing stability.

What should be considered about stability when using a tower scaffold with an internal staircase system instead of ladder access?

Answer: Staircase towers may have different height-to-base ratios and require specific outrigger configurations as specified by the manufacturer

Staircase towers often have different frame geometries and weight distributions compared to ladder-access towers. They may have different maximum heights, base-to-height ratios, and outrigger requirements, all specified in the manufacturer's product-specific manual.

What is the purpose of a ground-level exclusion zone around a tower scaffold?

Answer: To protect people on the ground from falling objects and from the tower in the event of a collapse

The exclusion zone protects people at ground level from tools, materials, or debris falling from the platform, and provides a safety margin in case the tower collapses. It should be barricaded and signed to prevent unauthorised access.

How does the number of people on the tower platform affect stability?

Answer: Each person adds weight at height, raising the centre of gravity and increasing both the vertical load and the overturning moment from their movements

Each person on the platform adds weight at height, raising the centre of gravity. Additionally, people move, shift weight, and can apply horizontal forces (leaning, reaching), all of which increase overturning moments. This is why safe working loads include personnel weight.