Often, technical guidance is good as far as it goes but can be unsuitable for non-standard problems. Wilf Butcher examines the precautions you need to consider when more than one system of fire protection is required on the same structural steel element.

Innovation in the structural design of buildings continues to present the designer and specifier with ever new challenges, when engineering appropriate fire protection solutions. Inevitably, therefore, questions will continue to be asked regarding the appropriateness of any particular solution, i.e. How can I be sure that the structural fire protection product or system I am specifying is appropriate?

The short answer to this question is that provided the product or system has been adequately tested under fire test conditions and assessed to an appropriate fire test standard – for example, BS 476 series, ENV 13381-4 or prEN 13381-8 – then the product or system may be considered as a means of enhancing the fire resistance of a structural steel member. However, perhaps a more appropriate question might be: How do the constraints of my structural design affect the tested and assessed product or system I intend to specify?

When specifying any product or system it is important to recognise that performance results awarded are a function of the system under test and the substrate to which it is applied. Therefore there are many conditions that will influence that appropriateness and the fire performance of any given product or system. These can include:

• the fire protection configuration to be adopted, e.g. boxed or profile
• the section's size and weight
• whether the section is to be protected on all sides or just the exposed faces
• the duration of the fire resistance required
• the failure, or limiting temperature criteria, that must be met
• the kind of fire protection system to be used.

Clear guidance on how to determine this is presented in the Association for Specialist Fire Protection's document Fire Protection for Structural Steel in Buildings 4th Edition (The Yellow Book).

Uninterrupted protection

All well and good so far. But this may not be the end of the matter, as there are other situations that that may not have been determined by practical test, for example, when a new type of fire protection material, or system, is being installed alongside an existing and alternative type of protection, on the same load bearing structural steel element; or where there is a need to refurbish the existing fire protection on part or all of a structure. In such situations the question becomes: How do I deal with the junction, to ensure uninterrupted protection?

In an ideal world, the ASFP considers it best practice to completely protect individual steel or structural elements of construction with the same fire protection system. While the fire testing and assessment process is extensive, the fire testing of all possible interfaces is impractical so, in general, the use of different passive fire protection systems on individual steel or structural elements of construction should be avoided. There are occasions, however, where the necessity to ‘butt joint' different systems becomes unavoidable, and in such circumstances it is essential to seek the advice and guidance of the respective product or system manufacturers. In so doing, one needs to be mindful of the following issues:

• The failure temperatures in fire are different for universal beams, cellular beams and universal columns, so the abutting systems should be suitably selected.
• The existing fire protection system, to be abutted or overlapped, must be fully cured and chemically compatible with any other system to be in contact with it.
• Overlapping, or abutting different systems needs careful consideration, since they may behave in different ways in fire. For example, ‘shrink back' of any system in fire, at junctions.
• The specific procedure will be affected by whichever fire protection system is first applied on-site and by the interval before a second system can be added.
• Who will be liable in the event of failure, and why?

The ASFP has now produced a Technical Guidance Document entitled Guidance on the junction between different fire protection systems when applied to load bearing structural steel elements (TGD 008) which addresses the above issues giving guidance on adding:

• spray coating adjacent to reactive coating
• spray adjacent to an existing spray system
• spray adjacent to existing board system
• a board system adjacent to reactive coating
• board adjacent to spray
• a board system next to an existing board system
• a reactive coating system next to either an existing reactive coating/board or sprayed system.

So, how do you address the refurbishment and upgrading of fire protection on structural steel? In the first instance there are three steps that need to be considered, namely:

[a] The fire resistance requirement of the structural steel frame must be established. This should involve contact with Building Control, or other relevant approval body and/or reference to Approved Document B: Fire Safety.

[b] Identify the existing fire protection system. Contact the manufacturer and assess the likely contribution to the required fire resistance, including the suitability of the existing system for continued use.

[c] Depending on the outcomes from [a] and [b], all areas and parts of the system which fail to be suitable should be repaired, over-clad, or removed and replaced with a system capable of fulfiling the new fire resistance requirements.

Given this scenario the specifier is faced with five options, namely:

• full removal and replacement
• repair/part removal and replacement with same system
• part removal and replacement with a different system
• over-cladding/refurbishment by adding extra thickness of same system
• over-cladding/refurbishment by adding protection using a different system.

The ASFP has also produced a Technical Guidance Document entitled Guidance document for the refurbishment and upgrading of fire protection for structural steelwork (TGD 010) which addresses this issue and the appropriate actions that can be taken. All of the above referenced documents may be freely downloaded at the ASFP website.