PASMA Stability and Outriggers 3 — Questions and Answers
Question 1: What is the danger of using a tower scaffold on a slope without proper precautions?
- There is no danger — castors handle slopes
- The tower's centre of gravity shifts towards the downhill side, dramatically increasing the risk of overturning (Correct answer)
- Slopes improve drainage and therefore safety
- The tower is more stable on slopes due to wedging effect
Correct answer: The tower's centre of gravity shifts towards the downhill side, dramatically increasing the risk of overturning
On a slope, the tower's centre of gravity shifts towards the lower side, reducing the restoring moment on that side. The adjustable legs must be used to level the tower, and brakes must be reliable. If the slope is too steep, the tower should not be used.
Question 2: What is the purpose of base plates on a tower scaffold?
- To make the tower look professional
- To distribute the load over a wider area and prevent the legs from sinking into the ground (Correct answer)
- To raise the tower above ground moisture
- To anchor the tower permanently
Correct answer: To distribute the load over a wider area and prevent the legs from sinking into the ground
Base plates spread the concentrated load from the tower legs over a larger area, reducing the pressure on the ground surface. Without them, the legs could punch into soft ground, causing the tower to become unlevel and unstable.
Question 3: What are sole boards and when should they be used?
- Sole boards are the platforms at the top of the tower
- Timber boards placed under base plates on soft ground to further distribute the load and prevent sinking (Correct answer)
- Sole boards are the lowest rung of the ladder
- Sole boards replace the need for castors
Correct answer: Timber boards placed under base plates on soft ground to further distribute the load and prevent sinking
Sole boards are timber planks (typically scaffold boards) placed under the base plates when the ground is soft, such as on grass, recently filled ground, or muddy surfaces. They further spread the load to prevent the tower from sinking unevenly.
Question 4: What happens to tower stability if one castor brake fails while operatives are working on the platform?
- Nothing — three brakes are sufficient
- The tower could roll or swivel on the failed castor, potentially overturning, especially if the operative is working at the platform edge (Correct answer)
- The tower becomes more manoeuvrable
- Stability improves because there is less friction
Correct answer: The tower could roll or swivel on the failed castor, potentially overturning, especially if the operative is working at the platform edge
A failed brake allows the tower to move on that castor. If an operative applies a horizontal force (e.g., reaching out), the tower could roll or rotate about the locked castors, leading to a loss of balance and potential overturning.
Question 5: Why should sheeting or tarpaulins NOT be attached to a tower scaffold without authorisation?
- Because they make the tower look untidy
- Because they dramatically increase the wind-catching surface area, increasing the overturning moment and risk of collapse (Correct answer)
- Because they add too much weight
- Because they obscure the guard rails
Correct answer: Because they dramatically increase the wind-catching surface area, increasing the overturning moment and risk of collapse
Sheeting, tarpaulins, banners, or any large-area material significantly increases the surface area exposed to wind, creating much greater wind forces. This dramatically increases the overturning moment and can cause the tower to collapse in even moderate winds.
Question 6: What is the significance of the 'narrowest base dimension' when calculating height-to-base ratio?
- It is not significant — use the widest dimension
- The height-to-base ratio is always calculated using the narrowest base dimension because the tower is weakest in that direction (Correct answer)
- Use the average of all dimensions
- Use the diagonal dimension
Correct answer: The height-to-base ratio is always calculated using the narrowest base dimension because the tower is weakest in that direction
The narrowest base dimension determines the tower's most vulnerable direction for overturning. A tower with a rectangular base will tip most easily along its narrow axis. The height-to-base ratio must be calculated using this narrowest dimension.
PASMA Stability and Outriggers 3
What is the danger of using a tower scaffold on a slope without proper precautions?