Combustible scaffolding materials could facilitate external fire spread, report warns

A new report from Collaborative Reporting for Safer Structures UK (CROSS-UK) has outlined recommendations to minimise the fire risk posed by scaffolding that features timber boards and plastic wrapping and which is erected around in-use buildings.

CROSS-UK has recommended that scaffold specifiers, building owners and contractors undertake a ‘holistic’ risk assessment when scaffolding that includes combustible materials is put up beside a building’s external face to ensure the risk of fire spread is evaluated effectively.

The independent body also suggests these stakeholders consider the potential for sheeting or other elements to negatively impact the performance of fire safety systems.

The report is relevant considering industry actions post-Grenfell to improve building safety standards, and was produced in response to a reporter’s concern that relates to the fire risk assessment process when scaffolding is erected around buildings in use, including those with sleeping occupants.

The reporter had highlighted the existence of "numerous residential buildings operating 'stay put' procedures [and] undergoing works that have [introduced] scaffolding formed of timber boards with plastic wrapping [and how this] could present a medium for fire spread". 

Aside from the contribution that [plastic] scaffolding wraps have on the heat release rate, an additional complication is that if the wrapping completely envelopes the building, it can affect the ventilation outlets’ performance, they warned. 

As CROSS-UK’s report outlines, "The reporter thinks that the wrapping can trap the smoke within the scaffold structure and spread it to other parts of the building if the scaffold structure is not adequately ventilated. This situation may inhibit smoke ventilation, not just from designated ventilators, but also through the windows and other openings."

Following on from this, the reporter felt that should this fire scenario arise, it would change the Required Safe Egress Time (RSET), lowering it due to the increased rate of external fire spread. Coincidentally, they also warned that were the smoke control system’s performance to be negatively affected, this would reduce the Available Safe Egress Time (ASET). 

"If the RSET extends beyond the ASET, then that creates a potential risk for the safety of the occupants," warns the reporter.

Fire risk assessment

CROSS-UK’s report says the reporter feels the construction industry is failing to properly assess the fire risk that arises from this issue and is also not taking reasonable steps to reduce the risk associated with scaffolding on in-use buildings.

Significantly, they feel industry stakeholders overlook the risk posed by a fire starting in a building and then spreading through the windows to the scaffold.

"This arguably ignores the most likely risk, which builds a false sense of security in the construction industry and is reinforcing potentially dangerous practice which can be encountered across the country."

The reporter also raises concerns regarding the fire risk assessments that Principal Contractors or their scaffolding sub-contractors undertake and questions whether the Health and Safety Executive (HSE) guidance HSG 168 is fit for purpose. Their argument is that it does not appropriately cover the fire hazards associated with the in-use areas of occupied buildings. 

"The construction industry needs to be aware that the fire risk assessment associated with an in-use building with a scaffold installation present will in many cases be a specialist task that requires involvement of competent fire engineers," the reporter argues. 

"This can be in much the same way as a PAS 9980 fire risk appraisal of the external wall (FRAEW) would be undertaken."

In the absence of any other guidance, they suggest PAS 9980 may present a suitable methodology for improving the situation. This is one of a list of suggestions they recommend (see box, below).

CROSS-UK’s Expert Panel has responded to the reporter’s concerns and agrees the subject is a concern.

Its panel notes that, under the Construction (Design and Management) Regulations 2015, the contractor should carry out a comprehensive risk assessment to ensure that the works they are undertaking do not present an unacceptable risk.

"If the building is occupied while the works are ongoing, then the risk assessment should include the occupants," they note. 

"That risk assessment should include issues such as the introduction of combustible materials during the works (e.g., scaffold boards, scaffold sheeting, or more) and try to ensure that the risk is reduced as much as possible. It should also consider the works methods (for example, if the works include removal of combustible insulation, where is it stored once removed?) and any other risks (for example, will the works affect any existing fire precautions, such as smoke vents?). This should be given serious consideration before any works start."

The panel also comments that HSG 168 has been updated and does provide some guidance on this issue.

Finally, it advises that while the contractor has responsibilities, the Regulatory Reform (Fire Safety) Order 2005 in England and Wales also requires the Responsible Person (RP) to consider these risks, holistically, and to work with the contractor so they are both aware of the risks posed and work together to minimise the impact.

"Given the potentially complex nature of the process, this will, no doubt, require the services of a competent person to assist the RP (and contractor), and also highlights the need for all stakeholders to meet and discuss these issues as early as possible," says the Expert Panel.

Reporter’s recommendations

The reporter proposed the following suggestions to assess and evaluate fire risk and consequently improve fire risk management:

• scaffold designers should be specifying non-combustible materials when possible and deemed appropriate, particularly where there is limited alarm provision to initiate an evacuation
• they should also acknowledge that the installation of fire detection and alarm systems that initiate evacuation procedures may reduce the risk in some cases, so the presence of vulnerable or disabled people also needs to be carefully considered, with appropriate evacuation arrangements to ensure that RSET is well below ASET
• they should carefully consider the issues raised in this report, namely the impact on smoke ventilation, not just from smoke ventilation systems, but also considering smoke and heat exiting the in-use buildings by windows, doors, and other openings in the external wall
• advice to the construction industry concerning the required level of competence of fire risk assessors who could carry out a suitable and sufficient fire risk assessment of an in-use building with scaffolding installed is required (this is a specialist task and a reference could be made to PAS 9980)
• the Health and Safety Executive (HSE) guidance HSG 168 should be revised to properly advise those planning and undertaking work on the holistic risk profile of the building, not just focusing on the risk on the scaffold itself; and
• the HSE and fire and rescue authorities should be informed and trained on these risks, to enable them to suitably participate in the safety. management system with the potential for enforcement where needed.

The full report is available to read here.