CU Phosco have received reports of instances where new floodlights have been installed on existing CU Phosco high masts without the appropriate checks being undertaken and the floodlight mounting bracket failing. In some instances, this has caused the floodlight to become detached from its supporting structure and fall to the ground, causing an immediate safety hazard to any personnel below. Depending on circumstances, there is also a risk of escalation from the broken floodlight causing damage to other equipment etc. and the possible additional safety hazards resulting from that damage.
In the latest incident a new flood light was attached to a single panhandle supporting bracket, causing the bracket to fail by fatigue, although in this case the failure of the bracket was spotted before it became fully detached from the supporting structure which prevented the floodlight from falling to the ground.
CAUSE OF FAILURE
The immediate cause of failure was fatigue of the bracket support, which was caused by the installation of the bigger and heavier new floodlight. The single pan-handle bracket was originally designed for our smallest and lightest floodlights, with a double pan-handle bracket being specified for our heavier floodlights. The floodlights installed in these instances exceed the design limitations of the existing lantern carriage.
The increase in weight and offset of the new floodlight, combined with the much larger, flatter form factor caused greater dynamic loading and cyclical stresses in the bracket, so reducing its fatigue life.
RECOMMENDED ACTIONS
It is essential when considering replacing floodlights on existing high mast lighting structures that the following check procedures are undertaken prior to floodlight specification and subsequent installation:
1. Confirm the high mast lighting structure is still within its design life.
2. Confirm the wind and gravity loading does not exceed that of the existing floodlights. This shall include consideration of the weight, windage area, drag and lift coefficients (at +/-5° from horizontal as required by BS EN 40 Sect. 5.3.4) and offset in loading from support point. Where there is an increase in any of the above items, the appropriate checks must be undertaken to ensure the proposed installation is within the capabilities of the existing bracketry.
3. Complete a full inspection for damage and deterioration, including NDT to inspect for possible fatigue cracking in the existing support prior to installation.
4. Where it cannot be shown that the existing supports are acceptable for the new floodlight, then consideration shall be given to the possibility of strengthening or replacing the existing supports.
Further to the above recommendations, it is noted that since 2007 CU Phosco have in all cases specified double pan-handle support brackets as a precaution to increase the integrity of our products where changes might be made during their life and to help ensure safe use beyond the original design life of 25years.
The above recommendations are specifically applicable to the local floodlight support brackets. This is in addition to normal industry requirements as stated in ILP PLG07 that where new floodlights are to be installed on an existing mast, the change in loading shall be checked. Where there is an increase in loading or if there is insufficient information to confirm the original design, then further structural design checks must be undertaken by a Chartered Civil or Structural Engineer to confirm the suitability of the structure with the new loading. This check must cover all parts of the mast structure, including the foundation studs, mast, lantern carriage, floodlight brackets and any raising and lowering system (if provided). This check should be carried out following an inspection of the mast and shall allow for any known deterioration.
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