PASMA Stability and Outriggers 4 — Questions and Answers
Question 1: What type of ground is most dangerous for tower scaffold stability?
- Concrete
- Soft, uncompacted fill or waterlogged ground that can settle or collapse under load (Correct answer)
- Flat asphalt
- Interlocking paving stones
Correct answer: Soft, uncompacted fill or waterlogged ground that can settle or collapse under load
Soft, uncompacted, or waterlogged ground can settle unevenly under the tower's weight, causing it to lean and potentially overturn. Recently excavated and backfilled ground is particularly dangerous as it may compact unpredictably.
Question 2: How should a tower scaffold be stabilised if it needs to be used near a building opening such as a window?
- Push it against the window frame for support
- Tie the tower into the building structure using proper fixings, if recommended by the manufacturer (Correct answer)
- Rest the outriggers on the window sill
- No special measures are needed near buildings
Correct answer: Tie the tower into the building structure using proper fixings, if recommended by the manufacturer
Tying a tower into an adjacent structure using appropriate fixings (wall ties) can significantly improve stability, effectively eliminating the free-standing height limitation. This must only be done if the manufacturer approves and the structure can support the loads.
Question 3: What is the risk of moving a tower scaffold with the platform loaded with heavy materials?
- No risk — the weight improves stability during movement
- The high centre of gravity makes the tower prone to overturning during movement, especially on uneven ground (Correct answer)
- Moving loaded towers is faster and therefore safer
- Heavy materials help steer the tower
Correct answer: The high centre of gravity makes the tower prone to overturning during movement, especially on uneven ground
Heavy materials on the platform raise the centre of gravity, making the tower top-heavy and unstable during movement. Uneven ground, bumps, or sudden stops can tip the tower. All materials and persons must be removed before moving.
Question 4: What happens to the stability of a tower scaffold during the assembly process?
- The tower is most stable during assembly
- Stability decreases as the tower gets taller, so the build sequence must maintain the base-to-height ratio at every stage (Correct answer)
- Stability is constant throughout assembly
- Assembly has no effect on stability
Correct answer: Stability decreases as the tower gets taller, so the build sequence must maintain the base-to-height ratio at every stage
As each lift is added, the tower gets taller and the height-to-base ratio changes. The assembly sequence must ensure that at every stage, the tower remains within safe stability limits. Outriggers may need to be fitted before the tower reaches its full height.
Question 5: Why must outriggers be deployed symmetrically around the tower?
- For aesthetic reasons
- To ensure equal stability in all directions — asymmetric deployment leaves the tower vulnerable to overturning in the unprotected direction (Correct answer)
- They do not need to be symmetrical
- To allow easier movement of the tower
Correct answer: To ensure equal stability in all directions — asymmetric deployment leaves the tower vulnerable to overturning in the unprotected direction
Outriggers must be deployed symmetrically to provide balanced stability. If outriggers are only fitted on one side, the tower has different stability characteristics in different directions, leaving it vulnerable to overturning towards the unprotected side.
Question 6: What is the relationship between wind speed and the force it applies to a tower?
- Force increases linearly with wind speed
- Force increases with the square of the wind speed — double the speed means four times the force (Correct answer)
- Force decreases with higher wind speed
- There is no relationship between wind speed and force
Correct answer: Force increases with the square of the wind speed — double the speed means four times the force
Wind force is proportional to the square of the wind speed. This means that doubling the wind speed from 10 mph to 20 mph quadruples the force on the tower. This is why relatively small increases in wind speed can rapidly make conditions unsafe.
PASMA Stability and Outriggers 4
What type of ground is most dangerous for tower scaffold stability?