In this article I will be discussing the general regulations surrounding the design and use of a personnel basket; more commonly referred to as a man basket. CSA Standard Z150-11 “Safety code on mobile cranes” gives a detailed outline of design requirements and operational guidelines for personnel baskets. This article will touch on the main points found in Z150-11.
General Design and Engineering Parameters
Firstly, the man basket shall be designed and approved by an engineer according to good engineering practice. The basket shall have design drawings that outline the size and specifications of all components used in manufacturing the man basket, including material type and grade, instructions for proper maintenance and inspection of the basket and the rated load of the unit. It must be manufactured and maintained according to these drawings. If the basket is welded it must conform to CSAW59 or AWS D14.3/D14.3M welding codes. Similar standards may be used provided they meet or exceed these mentioned welding standards. It shall only be modified or repaired according to the manufacturer’s specifications or under the direction of a qualified engineer.
The man basket platform shall have a minimum load rating of 300lbs (136kg); and as a general rule of thumb, 300lbs should be added for every person added to the maximum occupant rating. A two man basket should therefore have minimum load rating of 600lbs (272kg). The man basket platform should be capable of supporting, without failure, its own weight as well as a minimum of 5 times the rated load. The weight and rated load is to be permanently marked on the man basket.
A properly constructed manbasket should have a top rail, intermediate rail, toe board, either a full or lower barrier and a slip resistant floor with provisions for draining water. The top rail shall be 39in-45in above the floor and the intermediate rail an equal distance between the upper rail and the toe board. The toe board is to be 3.5in above the floor and around the entire periphery of the platform. The top rail, intermediate rail, and lower barrier shall be able to withstand a 300lbf concentrated load applied at any point in any direction without yielding the material.
Suspended Platforms vs Pinned Platforms
There are two types of personnel baskets: a suspended type that hangs from a hoist line using cable or chain rigging, and a pinned type that is pinned to the crane boom using a mechanical connection. Suspended platforms are subject to more requirements regarding the overhead rigging used to hang the basket while pinned baskets are subject to other requirements for the supporting frame.
A suspended man basket must be equipped with a secondary suspension that is tied off above the travelling block of the crane but must not interfere with the travelling block at all. This essentially acts as a backup tether should the hook fail or basket become detached. All wire rope and rigging components must be capable of supporting 10 times the intended load to be transferred to that component and all bridles and rigging must be identified and labeled for specific use only to lift personnel. The eye of any wire ropes are to be made with a flemish eye, thimble and mechanical splice, and there are to be no wire rope clips used in the rigging and no synthetic slings. The basket is to be designed so that the failure of one support would not cause the structure to collapse. Suspended baskets need to have a continuous handrail on the outer perimeter of the basket as well as a means to secure loose items within the platform. If the basket has a gate, it must have a means of locking the gate from accidental opening and must open inward unless size of the platform prevents inward opening. There needs to be designated and identified anchor points within the basket for personal fall protection, and the number of anchor points needs to be equal to or exceed the number of rated occupants. One anchor point can be designed to accommodate more than one person, although each anchor point must be able to withstand a 3600lb static force (per person) without failure. It is acceptable to tie off personal fall arrests above the crane hook, however a suspended man basket must still offer anchor points within the basket.
A pinned style man basket is one that utilizes a solid pinned structure attached to a crane boom. It is necessary for this connection to have a minimum safety factor of 2 on yield for ductile materials and 5 on ultimate for brittle materials. Pinned man baskets must be equipped with a device to keep the platform in a level position and must be guarded against overturning.
Crane Requirements for Operating with a Man Basket
When employing a man basket it is important that the crane being used is properly equipped for using the man basket. Generally a crane operating with a suspended or pinned basket shall be down-rated to half of the rated capacity and should have a boom with fail safe systems to prevent unintended collapse or lowering of the boom. The crane must also meet the other requirements outlined in the mobile crane safety standards.
Requirements specific to cranes using suspended baskets
The crane should be equipped with an anti-two blocking device as well as a locking device on the hook to prevent the basket from accidentally becoming detached. The hoist lines must be able to support 10 times the intended load and the winch should have power down capability. If the crane is equipped with a secondary hoist line, the line and rigging must be removed or set in a way that will not tangle with the workers platform and endanger the personnel.
Requirements specific to cranes using pinned baskets
Cranes using a pinned basket are to have the hoist line removed or set in a way that will prevent the line from endangering workers or interfering with crane operations. There needs to be anchor points on the crane boom for the personal fall arrests, no less than the number of allowed occupants. These anchor points are to be rated to the same static load of 3600lbf. Personnel in a pinned basket are to be tied off to the crane boom and not the basket.
All workers are to wear a personal fall arrest system that consists of a full body harness and a self-retracting lanyard or one fitted with an energy absorber. In the case of a fall the lanyard must not exert more than 1350lbs on the worker. The lanyard must be attached to the specified anchor points and must allow for movement around the platform with minimum lanyard slack. The fall arrest equipment must meet the following standards; CSA Z259.10, CSA Z259.11 and CSA-Z259.2.2
Before lifting personnel the crane should have all structural components inspected, be on firm footing, and be levelled and deployed according to manufacturer’s specifications. A trial lift needs to be performed before lifting personnel and the operator must remain at the controls the entire time the lift is in progress.
A preliminary lift must be performed with the basket loaded to the max rated load, with no personnel in it, to verify the all the systems, rigging, crane setup and lift routes. The trial lift shall ensure that the lift route is free from interferences and that the crane will remain under the 50% load in all configurations necessary. First the basket must be lifted 1m from the ground to verify the rigging and attachment to the crane, this must be done every time the basket is connected and reconnected to the crane. Second the platform needs to be lifted to each work location to verify the lift path and crane rating throughout the path and work locations.
It is my hope that reading this article gives a good understanding of the general design of man baskets as well as the basic operational procedures that need to be followed when deploying a man basket. For further information and more detailed accounts of design and operational requirements I would recommend reading through CSA Standard Z150-11 “Safety code on mobile cranes”.