Specifying fire protection for structural steel

Despite being a non-combustible material, steel can lose structural integrity in a fire, potentially leading to building collapse.

As test standards are based on common scenarios, this can present a significant challenge, especially for the Principal Designer as defined by the Building Safety Act.

What parameters do I need to consider when specifying fire protection for steel?

Structural steel can lose load-bearing capacity at temperatures between 350-700°C. In each instance, section factors, limiting temperatures, and specific requirements of each building element can be used to calculate the level of protection required, measured in minutes.

Promat fire protection boards are available in different thicknesses that correspond to minimum levels of protection for various limiting temperatures and section factors. This makes it relatively straightforward to specify a compliant solution in standard conditions.

What kinds of boards are available and what is the difference between them?

PROMATECT®-XW offers up to 60 minutes of fire protection. It is weatherproof for up to six months, allowing flexibility in construction schedules, and is a highly workable construction material.

VERMICULUX®-S is a premium product offering fire protection from 30 to 240 minutes for limiting steel temperature of up to 750°C. The board is lightweight and thinner compared to other fire-resistant constructions, maximising usable space.

PROMATECT^®-250 provides up to 120 minutes of fire protection. Incorporating autoclaved calcium silicate spheres, its high strength makes it suitable for the protection of mezzanine floors, and it is often used in warehouse applications.

What if steel is involved in compartmentation? 

Fire protection becomes complex for steelwork running along compartment lines. Current regulations can appear contradictory, as they must address both the prevention of fire spread and the maintenance of structural integrity. Note that intumescent paints may not provide sufficient protection to maintain compartmentation where steelwork forms part of a fire compartment.

What other circumstances require special consideration?

SFS interfaces and partition connections require particular attention, as they may carry significant loads. The absence of specific test standards for all scenarios necessitates a case-by-case assessment.

When dealing with brackets and connections, the ASFP Advisory Note 21 guidelines specify that penetrations of fire protective encasement by brackets should not exceed 3,000mm²/m, and recommend aligning bracket connections with board joints to minimise gaps.

Cellular beams typically fail at lower temperatures than solid equivalents. The asymmetrical nature of many cellular beams further complicates their protection requirements. Structural assessment under both ambient and fire conditions is essential, with limiting temperatures calculated from detailed structural models by specialists.

How can I make sure my solution is compliant?

The key lies in understanding the relationship between section factors, limiting temperatures, and required protection levels. Early engagement with fire protection specialists is crucial, particularly for projects that deviate from standard applications.

Third-party verified testing plays a vital role. At Promat we conduct additional, bespoke testing to validate solutions for specific applications. This includes testing for compartmentation requirements, interface details, and protection systems for cellular beams.

Technical support

Promat technical specialists are on hand to ensure any potential issues are flagged at the design stage and advise on the best course of action.

All of our specification and technical teams are qualified to, or working towards, the IFE Level 3 qualification in Passive Fire Protection. We also offer training courses on the application of passive fire protection, including structural steel to support competence across the sector.

Want to learn more? Download our Guide to Protecting Structural Steel > structural steel information request - Promat