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Safeguard OSH Solutions - Thomson Reuters

Safeguard OSH Solutions - Thomson Reuters



Safeguard Magazine

Incident investigation—Floor failure

Summary

A fire alarm technician died from head injuries after falling 10 metres when a section of a floor made from fire-stopping mortar collapsed under him.

CONTEXT

  • • 
    He was working in the plant room on the second level of a commercial building under construction.
  • • 
    A space had been boxed out in the floor of the plant room when the slab was poured to accommodate the HVAC ducting between the floors.
  • • 
    The HVAC design changed so a 1.0×0.5m section was not filled with ducting as planned.
  • • 
    Access to the plant room was mainly across this space in the floor.
  • • 
    Drawings showed this gap was fire-proofed and covered by a metal walkway.

DETAIL

  • • 
    Fire-stopping mortar had been poured into the gap and it was isolated by barriers and unsecured covers.
  • • 
    These were removed to allow HVAC risers to be installed, and from then on the gap in the floor was no longer isolated.
  • • 
    Loose planks were sometimes placed over it by contractors working in the plant room.
  • • 
    Other times – including this day – the mortar was uncovered and was walked over by contractors.
  • • 
    In the dimly-lit conditions the mortar looked like standard concrete flooring.
  • • 
    The permanent metal walkway in the drawings was never installed.
  • • 
    Immediately before the incident a ladder was set up on the mortar by another contractor and used to access the top of the ducts.
  • • 
    The alarm technician moved the ladder then stepped onto the mortar.

CONTRIBUTING CAUSES

  • • 
    The mortar was neither reinforced nor mechanically keyed into the surrounding floor slab.
  • • 
    The mortar had a high moisture content so was not performing to its specified strength.
  • • 
    Designers, contractors, installers and principals on the site had differing views about the expected structural performance of the mortar and the need to prevent any load being put on it.
  • • 
    Fire mortar has been widely used in the building industry for fire-stopping holes in floors, but has not been routinely isolated when installed.

BROADER LESSONS

  • • 
    A product used to fill a hole in a floor large enough to harm people must meet the loads detailed in the Building Code.
  • • 
    Any statements about the structural performance of a product should be verifiable. Information from suppliers should reference AS/NZS 1170.1:2002 Structural design actions – Permanent, imposed and other actions.
  • • 
    The design for the installation of a product in these circumstances should be reviewed by a competent person such as a chartered professional engineer.
  • • 
    The installation should be monitored and tested in accordance with the product’s specifications.
  • • 
    If a floor gap product does not meet the Building Code’s load bearing requirements it should be permanently isolated.
  • • 
    The need for isolation must be clearly communicated between designers, contractors and principals and the methods of isolation coordinated between all parties.
  • • 
    Permanent isolation should be in place at the earliest practicable stage.
  • • 
    Fire mortar products are typically, but not exclusively, found around hydraulic risers and HVAC ducting in floor penetrations.
  • • 
    Building managers and owners should seek expert advice to assess whether any mortar currently being used is suitable for load bearing.
  • • 
    It must be isolated if there is any doubt, because the product may have the appearance of a concrete floor.
  • • 
    Take special care during demolition or renovation as areas where the product is installed may have been permanently “walled in” at construction and may be exposed when walls are removed.
  • • 
    Fire mortar is part of the passive fire control system in a building and the integrity of that system needs to be maintained for fire safety.

Thanks to WorkSafe New Zealand for its assistance with this column.

Thomson Reuters

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