Boom MEWPs: working envelope, capacity and restraint
Boom MEWPs are the articulated and telescopic machines in categories 1b (static boom) and 3b (mobile boom). The exam tests how the boom envelope, load chart, stability and platform access interact, and whether you can explain why a machine that is within its platform placard can still be overloaded at a particular outreach.
The envelope governs everything
- A boom's rated capacity is not one fixed number; it depends on boom configuration, radius, boom angle and sometimes jib position. Read the load chart at the actual working position, not only the platform placard.
- Keep the platform inside the manufacturer's envelope. Do not use the boom to pull, push or drag loads, and do not tie the platform to a structure.
- Watch for crush points between the platform and fixed structures; the boom can move in several axes while the platform is close to a beam, pipe or ceiling.
Platform and fall protection
- In a boom platform, wear a full-body harness with an adjustable restraint lanyard attached to the designated anchorage. It is a restraint system intended to stop ejection from the platform, not a fall-arrest system.
- Never clip to the guardrail unless the manufacturer identifies that point as an anchorage.
- Keep gates closed, keep feet on the platform floor and do not climb on the guardrails.
Stability and ground
- Check ground bearing, slope and voids. For a 1b machine, deploy outriggers or stabilizers as specified and use spreader pads. Keep clear of excavations, trenches, drains and soft patches.
- Stop when wind exceeds the machine rating or when handling large sheet materials; the platform and load act as a sail.
- Treat overhead lines as live and maintain the required safe distance.
Worked example
A 3b telescopic boom has a platform placard of 230 kg. At 10 m outreach the load chart allows 120 kg. Two operatives weigh 85 kg each (170 kg), plus 20 kg of tools, giving 190 kg. The placard is satisfied but the load chart is not. The correct action is to reposition closer, reduce the load, or use a larger machine. Reasoning: the load chart reflects the moment on the boom at that radius, not just the weight on the platform floor.
Traps that cost marks
- Quoting maximum platform capacity without checking radius.
- Using a long fall-arrest lanyard instead of a short restraint lanyard.
- Moving a 1b base with someone in the platform.
- Assuming the normal wind rating applies when a large panel is on the platform.