The K Guard handrail system consists of five components which made the link bar: external sleeve, internal sleeve, rat’s tail, captive bolt and captive nut.
While temporarily removing the edge protection, the external sleeve section of the link bar (top handrail) became dislodged from its internal section and fell five floors below into the exclusion zone set up for these works.
Upon investigation and assessment of the cause of this incident, Sir Robert McAlpine were able to advise the manufacturer that this product presented a possibility for human error at the assembly line and requires redesigning to eliminate this to guarantee that the sleeves would not physically be able to become detached whilst allowing adjustable lengths.
The first element to the new design is that the insert has been form-pressed at one side in the middle of the insert (groove). At this section, the locking mechanism works once the nut has been welded in the external sleeve.
The second element to the new design is the introduction of a 21mm bolt and nut system, welded inside the outer sleeve. This nut forms a physical wedge inside the outer sleeve, even if the bolt is missing, the two sections (outer sleeve and insert) will not come apart. The bolt is tightened with a 21mm spanner. It is now impossible for the insert to become detached from the external sleeve.
K Guards Works procedure and works cards have been changed. The new Quality Check form has been amended to suit manufacturing process and testing of the new design. The new human element in the assembly line is the quality of the weld as only the external section of the nut can be welded. Training for installation remains the same.