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The principal designer's role in preventing failure

07/06/2019 - 12:48PM

The Principal Designer Role on Demolition and Refurbishment Projects

The Health and Safety Executive have published some learning points in relation to a number of case studies of incidents that have occurred on demotion and refurbishment projects(1).  This paper seeks to explore how the Principal Designer might have acted, in their role as Principal Designer, to prevent the incidents.  It is not suggested that the Principal Designer should have exceeded their statutory role.  This paper needs to be read in conjunction with the original paper.

The actions that a Principal Designer should take are defined in the Construction (Design and Management) Regulations 2015, predominantly in regulation 11.  How the Principal Designer (PD) acts is informed by their skills, knowledge and experience (SKE) and the particular circumstances of the project.  The following observations are based upon the limited information that is provided in the case studies.  It is not known if any of the actions identified were initiated by the PD and subsequently ignored by other members of the team.

The themes that arise from an examination of these case studies are that either the Principal Designers did not have the appropriate skills, knowledge and experience; they lacked the ability to make the client or designer take what would have been appropriate action; they did not exercise their responsibility over all the design.  This resulted in inadequate PCI and/or a failure to communicate information about risk.

In making this statement it is recognised that on each of these projects there would have been a principal designer, either formally appointed or by default in the absence of an appointment in writing.  For those projects that had commercial clients the PD role would have defaulted to the client, the company contracting the works if they did not make a formal appointment.  For those projects that had domestic clients, in lieu of a formal appointment, the PD role would have defaulted to the designer, whether that be an entity trading as a designer or the contracting company who, prior to carrying out the works, ‘designed’ the solution.

Case Study 1 Premature collapse of high rise residential block during demolition
The Principal Designer should have recognised that the pre construction information provided by the client was insufficient.  A PD with appropriate SKE should have known the concern with the construction of pre cast panelised residential towers (see Ronan Point) and should have requested that investigations were carried out into the integrity of the connections.  It would be nice to think that the PD worked with the designers of the demolition solution and encouraged the principle of the use of a long reach machine and large exclusion zone to remove operatives from harm’s way, but this was probably a contractor decision.

Case Study 2 Basement collapse
The Principal Designer should have worked with the designer to ensure that one safe way of carrying out the works was identified and the significant residual risk of not following the underpinning sequence was identified in designer’s design risk management documentation and communicated to the contractor via the pre construction information .  A PD with adequate SKE should be aware of common unsafe practices by some basement contractors which should have informed the designer’s judgement about what was a ‘significant’ risk.  There also appears to be a failure on the PD’s part to ensure that there was adequate pre construction information in relation to underlying strata.

Case Study 3 Contractor competence
The Principal Designer with the correct SKE should have worked with the designer to ensure that the designer specified the correct foundation type given the risks and the anticipated nature of the capabilities of the contractor.  The designer’s residual risk information in the pre construction information should have made the risk of collapse clear.

Case Study 4 Failure to correctly assess existing structure
The Principal Designer failed to ensure that there was adequate pre construction information which would have informed the contractor/designer of the structural form.  It would not be reasonable to suggest that this was a lack knowledge or experience of the possible structural forms, PDs are not required to be design discipline experts, but there was a lack of skill to recognise that the structural form should have been identified to allow an adequate demolition design to be carried out.

Case Study 5 Temporary load on existing structure not assessed
The Principal Designer should have recognised that the plant would need to be moved from floor to floor and should have had adequate experience to know that the method that was adopted on this project is a common one as it removes the need to have a crane in attendance.  This should have led the PD to identify this risk to the designer and to ensure that the designer’s response was appropriate whether that was picking a design solution that had back propping or identifying the restricted floor capacity as a residual significant risk.

Case Study 6 Failure to consider implications of removing cross walls
The Principal Designer should have identified that there might be a temporary stability issue and asked the question of the designers.  This should have resulted in either the design being modified or the temporary instability being identified in the pre construction information as a residual significant risk which would have prompted the contractor to consider it in the design of his work method.

Case Study 7 Support provided by non-loadbearing elements
In this case it is difficult to see what the Principal Designer should have done.  It might be argued that a Principal Designer with adequate experience of working on these types of buildings might be aware that historic movement of the brickwork puts loads into the window frames.  This might have been evident from a full structural survey which might have revealed cracking, prompting questions about stability of the structure.  It might be argued that a Principal Designer working on this type of building should ask the designers “do we know how the load paths work in this structure” but this might just be a suggestion prompted by hindsight.

Case Study 8 Load bearing elements removed during soft strip
In this case it is difficult to see what the Principal Designer could have done.  Should the PD have asked if adequate information was available or is this just hindsight.  A structural engineer with appropriate SKE should either have been aware that this building form relied upon panel action or should have asked themselves how the building worked structurally as it would have appeared that there was a shortage of bracing, prompting the question about panel action.  The assessment of the SKE of designers is the clients responsibility prior to appointment and the designers’ responsibility before accepting a commission.

Case Study 9 Agreed sequence not followed causing scaffold collapse
The designer should have identified that a residual significant risk was that the sheeted scaffolding should be struck as the demolition progressed and if they did not the PD should have asked the question; scaffolding collapses are sadly not rare and the presence of sheeting and insufficiency of tying are usually implicated.  When the significant risk had been identified the Principal Designer should have communicated this in the pre construction information.

Case Study 10 Existing structure overloaded by removed materials
The Principal Designer with the appropriate SKE should have asked the question about the structural capacity of the floor and the amount of bricks that could be stored on the floor and communicated this significant risk in the pre construction information so that the contractor could have chosen to store the bricks elsewhere or to commission the design of a back propping scheme.

Case Study 11 Designer instructions not clear and contractor too keen.
The Principal Designer should have asked a question about the soil strength and, when it was identified that it was not known, had the gap in the pre construction information filled with simple soil strength information.  This would then have led the PD to identify to the designers the risk of deep excavation and other foundation options that the designers could have chosen.  Even if it was expected that the strip footings were only going to be one metre deep their proximity to the existing building should have promoted the PD to identify that the pre construction information was lacking and get information about the depth of the foundations of the existing building.  As excavation was required, the PD should have identified that the pre construction information was incomplete if there was no information about buried services.

Case Study 12 Unchecked change to system of work caused collapse
It appears that the structural stability of the cinema was sensitive to the demolition method.  The Principal Designer should have understood this from interaction with the designers and communicated this in the pre construction information.  The Principal Designer should have made it clear that any design needs to be brought to the attention of the Principal Designer.  There was a change in the design of the demolition and this should have brought to the attention of the Principal Designer.  It is recognised that this does not always happen.

(1)  Green, J., “Ensuring Structural Stability during Demolition and Refurbishment Work” Health and Safety Executive, 14 May 2019, https://press.hse.gov.uk/2019/05/14/ensuring-structural-stability-during...

Source: APS