The Western Australia Department of Consumer and Employment Protection(DOCEP) has released a Significant Incident Report after segments of a 100 m long underground ladder were found in a twisted and broken pile at the bottom of an escape ladder rise to surface.
About 45 m of ladder were found at the base of the rise.
The ladder was constructed of galvanised tubular steel sections and manufactured in a modular system for ease of installation from the top of the vertical rise using a crane.
As is quite common in the area, the rise was subject to localised inflows of hypersaline water.
The ladder was installed only four years prior to its failure. There was no substantive corrosion on the modular sections recovered from the bottom of the rise.
Immediate causes and contributing factors include a significant amount of salt build up from the material at the bottom of the rise. This would have added to the total load suspended from the ladder mountings.
The apparent failure may have also been associated with breather holes in the ladder sections, which are required for cooling and moisture removal during the hot dip galvanising process.
The ladder modules have three main structural elements (standard side-by-side step-over ladder arrangement). Internal corrosion in one structural element could cause the load on the ladder to exceed the load carrying capacity of the adjacent components.
According to the Report, an in-depth inspection should be carried out of all escape ladderways to check for and monitor internal and external corrosion. Care should be exercised during the examination process in case it causes traumatic failure of a ladderway component weakened by corrosion.
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