Mast Climbing Work Platforms

A mast climbing work platform (MCWP, or mast climber) is a work platform that travels up and down a vertical mast on a rack-and-pinion drive, powered by electric motors. They carry people, tools and materials on the sides of tall buildings, such as for bricklaying, curtain wall, cladding and facade work. They are efficient, but a failure, an overload or a poor tie-in can be catastrophic.

• Masons
• Facade & Cladding
• High-Rise Construction

How they work

• Mast sections are bolted together to the needed height and tied to the building. The platform runs up the mast on a rack-and-pinion drive.
• Platform sizes vary, and some are extendable. Single-mast and twin-mast units are common, and some can be stepped or fitted around corners.
• Safety devices include emergency stops, limit switches, an overspeed or anti-fall device that locks the platform if it drops, and a brake on the drive. Doors and gates stop people from entering the platform at the wrong level.
• The industry standard for design and safe use of these machines is ANSI/SAIA A92.9, and the maker’s manual and load charts control how it is set up and used. For construction, OSHA’s scaffold and general rules apply, and the employer must follow the manufacturer’s instructions. See Scaffold Basics and Aerial Lifts.

Planning and setup

• Plan the job with a competent person and an engineer where needed: location, height, tie-in points, loads, power supply, access and rescue.
• Check the ground. The base must be firm, level and able to carry the combined load of the machine, platform, mast and materials. Use mats or engineered pads as needed, and don’t set it up near open excavations or basements without checking.
• Check the building. Tie-in points must be strong enough for the ties, and the structure must be able to take the loads. Ties go in at the spacing and with the free-standing height limits the maker specifies.
• Assemble per the manual. Only trained, authorized people may erect, extend, tie in and dismantle the machine, with a competent person supervising. Use correct bolts and torque, and don’t mix parts from different makers.
• Power supply: use properly rated cords and GFCI protection, with cords supported and protected. Keep clear of overhead lines. See Overhead Power Lines and GFCI Protection.
• Protect the area below: barricade the ground area and keep people out of the fall zone. See Hard Hats.
• Ground the machine and keep it away from live power sources.

Loads and limits

• Know the rated capacity of the platform, including the number of people and the weight of tools and materials. It’s on a plate and in the manual. The rating may depend on platform length, and on how loads are spread.
• Don’t overload. Bricks, block, panels and stone are heavy. Weigh materials where there is doubt. Spread loads evenly and not at one end.
• Watch wind. There are maximum wind speeds for use, which decrease as the platform goes higher and as panels or sheeting add sail area. Stop work and secure the machine when winds exceed the limit. See Scaffold Weather.
• Don’t exceed the free-standing height and tie spacing rules, and don’t use the platform for hoisting or as a crane unless the manufacturer allows it.
• Don’t modify the platform, add extensions or attachments, or enclose it with banners or sheeting without engineering approval.

Working on the platform

• Get trained. Operators and users need training on the machine, its controls, hazards, load limits, fall protection and emergency procedures, with familiarization on each model. See Training Requirements and Aerial Lifts.
• Inspect before each shift: check the mast and ties, rack, bolts, drive, brake, limit switches, anti-fall device, gates, guardrails, cables, controls and emergency stops. Remove from service if there are defects. Have a competent person do frequent and annual inspections, as the maker requires.
• Use guardrails and gates properly. Keep gates closed while the platform moves, and keep the guardrail system complete. Use fall protection as the plan and rules require when working outside the rails, and when erecting or dismantling. See Personal Fall Arrest Systems.
• Keep hands and body inside when moving. Watch for pinch points between the platform and the building or mast.
• Keep the platform clear of debris and slippery material, and stop work in lightning, high winds or other bad weather.
• Keep the work platform close to the wall as the maker allows, and mind gaps between the platform and the structure. Cover or guard gaps.
• Use only one person to control, and communicate by radio or signals with those below and at landings.

Loading and unloading at landings

• Landing and loading areas must be strong and protected. Use gates, ramps and guards so there is no open edge between the platform and the floor.
• Don’t overload the floor slab of the building or place heavy loads at the edge without checking its capacity.
• Use carts and equipment sized for the platform, and secure loads against sliding.
• Keep people out from under the platform and from the landing area while loads move.

Emergencies and rescue

• Know the lowering procedure. If the machine stalls, workers can often be lowered by an emergency descent system, a manual brake release or the maker’s procedure, done by trained people only.
• Have a rescue plan for workers stuck at height, in case of power loss, mechanical failure or a worker fall. See MEWP Rescue and Fall Rescue.
• Stop and report unusual noises, jerky movement, overspeed trips, damage or a failed safety device. Take the machine out of service, and don’t restart until it’s repaired and inspected.
• If the anti-fall device activates, don’t reset it yourself. Follow the maker’s procedure.

Mast climber checklist

• A competent person planned and supervised erection; the base, ties and power meet the maker’s requirements
• Users are trained and know the rated load, number of people and wind limits
• Pre-shift inspection of the mast, ties, drive, brake, limit switches, anti-fall device, gates and rails is done
• Guardrails, gates and fall protection are in place; the area below is barricaded
• Landings and loading areas are guarded, and the building can carry the loads
• A rescue and emergency lowering plan is ready

Last updated: October 5, 2026