PASMA Stability and Outriggers

Question 1

What is the maximum height-to-base ratio for a mobile tower scaffold used outdoors?

Accepted Answer

3:1

Answer

For outdoor use, the maximum height-to-base ratio is 3:1, meaning the tower height must not exceed three times the narrowest base dimension. This accounts for the additional wind loading that occurs outdoors.

Question 2

What is the maximum height-to-base ratio for a mobile tower scaffold used indoors?

Accepted Answer

3.5:1

Answer

For indoor use, the maximum height-to-base ratio is 3.5:1. The higher ratio is permitted because indoor towers are sheltered from wind. However, doors, openings, and internal air movement should still be considered.

Question 3

How do outriggers improve the stability of a tower scaffold?

Accepted Answer

They increase the effective base size, thereby improving the height-to-base ratio

Answer

Outriggers extend the effective base footprint of the tower. By increasing the base size, they improve the height-to-base ratio, allowing the tower to be used at greater heights while maintaining stability against overturning.

Question 4

What must outriggers rest on to be effective?

Accepted Answer

Firm, level ground with base plates to spread the load

Answer

Outriggers must make firm contact with the ground through base plates that spread the load. If the ground is soft, sole boards may be needed under the base plates. An outrigger resting on soft ground can sink, rendering it ineffective.

Question 5

What is the main force that causes a tower scaffold to overturn?

Accepted Answer

A horizontal force (such as wind or pushing) that creates a turning moment about the base edge

Answer

Overturning occurs when a horizontal force (wind, operatives leaning out, impact) creates a turning moment (torque) about the base edge that exceeds the restoring moment from the tower's own weight. The wider the base, the greater the restoring moment.

PASMA Practice Test

PASMA Practice Test

PASMA Stability and Outriggers