ASFP releases new advice on the fire protection of structural steel and firestopping seals

The Association for Specialist Fire Protection (ASFP) released a suite of new Advisory Notes in July 2020. The first four are in relation to the fire protection of structural steel, while it has also produced a new Note on the Compatibility between Pipes and Acoustic or Firestopping Seals. This article has since been updated with further advisory notes on the fire protection of structural steel in August 2021, which are identified where appropriate. 

Advisory Notes on Fire Protection of Structural Steel

The four new Advisory notes address specific concerns identified by industry.

ASFP Advisory Note 18: ASFP Position on Installing Partitioning to the Underside of Structural Steel Sections Coated with a Reactive Fire Protection System

• This note highlights concerns related to fixing partitioning directly to columns or beams treated with intumescent paint. It notes that fixing anything directly to either the column/beam will impede the intumescent paint from expanding and may allow heat to transfer to the steel, resulting in localised loss of strength and potential failure in the event of a fire.
• Since partitioning is often installed along the line of a structural steel frame, the ASFP has joined with the FIS (Finishes and Interior Sector – the dry lining industry trade association), to recommend that, regardless of the existing sound or acoustic protection, the beam or column should be boxed out with an independently tested framed or an unframed system that will provide the required level of fire protection to the beam/ column.

Advisory Note 19: ASFP Position on the Use of Critical Steel Temperatures above 650°C

• This recommends that if a limiting temperature of above 650°C is specified, then a second opinion should be sought from an appropriately trained structural engineer. This reinforces the best practice guidance contained within Advisory Note 12: Best Practice Guide for Specifying Reactive Coatings for Structural Steel Fire Protection, published jointly by the ASFP and the British Coatings Federation.

This advisory note was updated with the following in August 2021:

• It highlights that it is vital to ensure that the appropriate limiting temperature is used in the specification of a reactive coating. Use of an elevated temperature (above 650°C) without the appropriate engineering checks could potentially leave a structure under-protected in a fire situation.

ASFP Advisory Note 20: ASFP Position on Portal Frame Buildings

• This note offers advice on providing fire protection to portal frame rafters, and should be used in conjunction with the SCI document P313: Single Storey Steel Framed Buildings in Fire Boundary Conditions.
• It recommends that where fire protection is required to portal frame rafters, certified 4-sided beam thicknesses should be applied to all 4 sides of the rafter, using the appropriate critical temperature.  In cases where a portal frame rafter cannot be coated on the top flange if the roofing materials are in place, a structural engineer and/or fire engineer should be consulted, as further action may be required. Care should also be taken to use the appropriate 4-sided section factor in all cases.

ASFP Advisory Note 21: ASFP Position on Coatback with Respect to Unprotected Secondary Beams Fixed to Protected Primary Beams

• Note 21 advises against the omission of coatback to protect secondary beams when the primary beam is fire protected. It describes references to such omissions contained within Steel construction – Fire Protection, published by the British Constructional Steelwork Association in 2013, as unconservative. The recommendations in the advisory note has more detail than that contained within ASFP Yellow Book (5th edition) and ASFP TGD 8: Code of practice for junctions between different fire protection systems which will be amended accordingly.
• The Yellow Book will state: ‘If there is no evidence to support the omission of coatback then a figure of 500mm as stated in ASFP TGD 8 Code of practice for junctions between different fire protection systems when applied to load bearing structural steel elements should be assumed as a conservative solution.’
• The guidance highlights that the primary beam must be a solid web beam and that omitting coatback does not apply when the protected beams are cell beams. While noting that individual manufacturers have undertaken tests to show that reduced coatback may be sufficient, the guidance states that the specific end use situation and the proprietary evidence must be considered and that coatback should only be omitted in situations where a detailed engineering study has been completed.

The following two advisory notes (23 and 24) were introduced in August 2021 by the ASFP.

ASFP Advisory Note 23: ASFP Position on Secondary Steelwork

• This provides advice on the protection of secondary steelwork, offering a useful flowchart to assist in determining whether protection is necessary and how best to provide it in different scenarios. The document defines what is deemed to be primary and secondary steelwork. It advises that steel bracing members required to provide stability to the structure at the fire limit state should have adequate fire resistance unless alternative load paths can be identified.
• The Note recommends that Project Design Teams and/or Structural Engineers review all available advisory documents regarding the need for the provision of fire protection for secondary steelwork, stating that this is not the responsibility of the fire protection installers or manufacturers of fire protection systems. It states that the Steelwork Designer should be consulted to identify Primary Bracing versus Secondary Elements highlighting that, where doubt exists, the assumption should be that the bracing is a Primary member and full protection provided. Where fire protection to secondary bracing members is necessary, the protection thickness should be based on the section factor of the member or a value of 200 m^-1, whichever is the smaller value.
• Where the actual section factor is less than 200m^-1, then the corresponding limiting steel temperature should be in accordance with the Column default temperature for Eurocode or British Standard designs as per ASFP guidance in Tables 16-18. Where the actual section factor is greater than 200m^-1, a section factor of 200m^-1 should be used  and a limiting steel temperature of 500°C. For all Secondary Element members, the protection thickness should also be based upon the appropriate Column data set (I section or Hollow section). The document provides guidance on scenarios where it might not be necessary to apply fire protection to Bracing members.

Advisory Note 24: ASFP Position Paper on the use of Yellow Book Critical Temperatures for the UK (or equivalent) Market

• This guidance note offers a range of proposals aimed at updating certain tables in the fifth edition of the ASFP’s Yellow Book: Fire protection for structural steel in buildings.
• The 5th Edition of the Yellow book was published to enable adoption of new European testing and Assessment methods – alongside amendments to the pre-existing UK test and assessment methods.
• In 2014, the ASFP introduced three new tables (Tables 16-18) of default temperatures in the Yellow Book, covering both the historical BS 5950 and newer Eurocode design scenarios. These tables were accompanied by a flow chart to help specifiers chose the correct table. However, these were considered over complicated, and have now been reviewed to offer clearer and easier to understand guidance.
• Advisory Note 24 introduces the proposed revisions. It highlights the importance of understanding and using the correct Codes and Occupancy (Building Category) in the design process as these can have a significant effect on the Critical Temperature of a steel frame; and consequently on the required thickness of Intumescent coating. It states that if the use of the building is not known, whether using BS 5950 or Eurocode, use of the Storage Category should be adopted.

Advice on compatibility between pipes and acoustic or firestopping seals

In addition, the ASFP has produced an Advisory Note on the Compatibility between Pipes and Acoustic or Firestopping Seals, which provides recommendations to ensure that all components perform as required.

The new advice highlights two significant compatibility issues relating to: the installation of short metal pipes that are to be connected later in the build programme; and the installation of sound and firestopping products with cPVC sprinkler pipes.

The Advisory Note highlights that when short metal pipes which run through penetration sealing systems such as collars, wraps and mastics (firestopping) are connected using soldering techniques, there is a risk of activating the firestopping. It recommends ensuring that where hot works are being carried out in proximity to firestopping systems, adequate insulation is provided to protect the firestopping.

The second issue relates situations where cPVC sprinkler pipes are used in contact with sealants providing a firestop, thermal or acoustic seal. Certain plasticisers common in sealants can migrate into plastic pipes causing the pipe to weaken and eventually fracture under pressure, leading to an escape of water and resulting flood damage.  Such migration can also occur when any material containing plasticisers, such as adhesives or materials within collar/sleeve devices, is in contact with cPVC sprinkler pipes.

The ASFP recommends that where two or more systems come into direct contact, the system owners are informed and that written evidence is supplied confirming the systems’ compatibility and long-term suitability.

The above issues were highlighted during work conducted by the ASFP, the Building Engineering Services Association (BESA), the Building Services Research and Information Association (BSRIA), Finishes and Interior Sector (FIS), the Gypsum Products Development Association (GPDA and UL to produce a new guidance document to address service penetrations in buildings. Drawing on the experience from many sectors of the construction industry, from those who work on partitioning, to the passive fire sector, the new guidance document will be published later this year.

All ASFP guidance documents are available for free download from the Publications area of the ASFP website.

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