HSE writes “open letter” to the structural timber industry

Open letter to all parties involved in the design, specification, procurement and construction of timber frame structures

The purpose of this letter is to explain HSE’s expectations in relation to the management of fire risks prior to and during the construction of timber frame structures. The letter has been produced in cooperation with the Structural Timber Association (STA), which represents the industry’s manufacturers and suppliers. STA and HSE are working together to promote a better understanding of fire risk management throughout all parts of the supply chain, including those outside STA’s membership.  The standards to be achieved are the same regardless of trade body membership or otherwise. 

HSE’s approach to off site fire risks during the construction phase of timber frame structures

Fire precautions during the construction of timber frame structures fall within HSE’s remit.  For any project, regardless of the construction method, duty holders have legal responsibilities to ensure the safety and health of workers and those who might be affected by their work activities, including those arising from fire risks.  Serious incidents have arisen where fires involving timber frame structures under construction have affected neighbouring buildings. Consequently, HSE has worked with the STA to produce guidance on reducing the risk of harm to people in buildings adjacent to the construction site.


All those making design and procurement decisions that significantly affect fire risk should consider and reduce the risk and consequences of fire during the construction phase through DESIGN. Failure so to do may constitute a material breach1 for which HSE will apply its Fee for Intervention scheme those duty holders who have contributed to the breach.

Detailed Explanation

Regulation 11 of The Construction (Design and Management) Regulations 2007 (CDM)requires risks to be considered and eliminated/reduced so far as is reasonably practicable through the design process.  This duty is imposed on anyone who makes decisions affecting the design, including, for example, architects, structural engineers, clients, suppliers, principal and other contractors and even those involved in the planning approval process where they specify particular construction methods or products.  This is explained in HSG 168 Fire in Construction, Appendix 4 http://www.hse.gov.uk/pubns/priced/hsg168.pdf 

The primary legal responsibility for assessing off-site fire risk rests with those making design and procurement decisions before work starts on site.  Designers and manufacturers of timber frame structures duties under CDM Regulation 11 cannot be passed on to the Principal Contractor.  Risk should be designed out as far as is reasonably practicable and information about residual risk passed to the Principal Contractor.  The Principal Contractor is obliged to consider and manage risks arising from the activities under their control at the site stage.   

The STA’s publication ”Design guide to separating distances during construction”http://www.structuraltimber.co.uk/information-centre/information-centre/technical-library/site-safe/ has been produced with HSE’s input and provides guidance on assessing the off site fire risk from timber frame structures under construction.  Although the title of the document “Design Guide to Separating Distances During Construction” might imply that the guidance is for use during construction, it is intended to be used at the design and procurement stages of a project. 

HSE commends the STA for the substantial work carried out to produce this guidance, promote its use and make it freely available to all rather than being restricted to STA members.  Although following the guidance is not compulsory, it does provide a practical means of complying with legal requirements. If an alternative approach to the guidance is used, a competent person with fire engineering qualifications and experience will need to determine the risks and to identify appropriate controls.  The persons involved should justify their decsions and recommendations in terms of risk, rather than cost.

Evidence from recent HSE inspections indicates that the risk of harm to occupants of neighbouring buildings from fire during the construction phase is not always effectively managed through either of the options above, and that not all duty holders understand what is required of them.

For a proposed structure, the STA guidance enables minimum separation distances to be determined.  Where space does not provide the separation distances required for a Category A structure, it provides guidance on selecting alternative timber frame structures to provide an adequate level of fire protection to neighbours during the construction phase. If a Category B or C structure or alternative fire engineered solution is needed, then it should be specified when the timber frame is being procured. Everyone in the supply chain has a responsibility to work towards this end.  Anyone in the supply chain who makes a decision, which significantly affects fire safety during construction, should be prepared to justify that decision.  If fire safety considerations are left to a late stage in the design development of the project, there is an increased potential that the solutions will be inconsistent in approach and less effective if there is a fire, and more time consuming and expensive to implement. Appropriate mitigation methods should always be developed before construction work starts on site. 

In practical terms HSE expects:

  • An assessment of the particular site and its constraints when the method of construction is being considered.
  • For timber framed structures, assessment can be undertaken using STA’s ‘Design guide to separating distances during construction’.
  • The assessment should identify that where there is insufficient separation distance to allow a Category A structure, the appropriate level of Category B or C to match the site constraints (unless an alternative fire engineered solution is developed by a competent person) should be recommended.
  • The appropriate category frame should be specified to the manufacturers. 
  • Timber frame manufacturers, including non-STA members have a significant role to play in ensuring appropriate specification and procurement of frames. Manufacturers should be advising their customers of the guidance and requirements. Use of the STA audit checklist may assist manufacturers in compiling records to demonstrate the steps they have taken to discharge their obligations under CDM Regulation 11 and record who has made specific decisions.
  • Any specific information and instructions that must be followed to guarantee the specified category or approved solution to be achieved on site must be passed to the Principal Contractor.
  • The Principal Contractor must adhere to the conditions required to achieve the specified category of structure.
  • The Principal Contractor must devise and apply appropriate fire precautions during the build, including control of hot works, provision of fire warning and extinguishing systems, provision of means of escape etc. 

HSG 168 was published in October 2010 and version 1 of the STA’s (then UKTFA) guidance was published in Dec 2011. Sufficient time has elapsed that knowledge and application of the guidance should now be embedded.  HSE inspectors expect duty holders to comply with CDM Regulation 11 using this guidance to assist.  Where a duty holder chooses not to follow the STA guidance but to implement a fire-engineered solution, standards of the equivalence to the guidance should be adopted. Duty holders should expect that in the latter circumstances, if lower standards are adopted then HSE may consider there to have been a material breach of health and safety law attracting charges under our Fee for Intervention Scheme http://www.hse.gov.uk/fee-for-intervention/index.htm.

Simon Longbottom

Head of Construction Sector and Policy

1 Material breach is defined in Fee For Intervention Scheme.

Article source: http://press.hse.gov.uk/2014/hse-writes-open-letter-to-the-structural-timber-industry/