How do EN10210 steel hollow sections perform under fire conditions?

When a fire breaks out in a building, bridge, or offshore platform, the structural hollow sections that hold everything together are asked to do something they were never tested for at the mill: maintain load-bearing capacity while the temperature around them climbs past 500 °C, then 700 °C, and beyond. For engineers and specifiers using EN 10210 hot-finished structural hollow sections, understanding how this standard's products behave under fire is no longer optional. It is part of writing a defensible specification.

EN 10210 governs hot-finished structural hollow sections in circular, square, rectangular, and elliptical forms. Because the steel is formed above 580 °C, the finished section has a uniform, recrystallized grain structure and low residual stress. Both of these metallurgical features turn out to matter when fire exposure is on the table.

This guide explains how EN 10210 sections behave when temperatures rise, what governs their fire resistance rating, and how to specify them correctly for fire-critical projects.

Why EN 10210 Sections Behave Differently in Fire

The fire behavior of a hollow section is driven by three things: the steel grade, the section's geometry (especially the section factor Am/V), and any applied fire protection. EN 10210's hot-finishing route influences all three.

Hot finishing above 580 °C refines the grain structure and relieves the residual stresses that would otherwise be locked into a cold-formed equivalent. In a fire, this means:

More consistent strength reduction as the section heats up, because properties are uniform through the wall.
Better low-temperature toughness to begin with, which translates into a more predictable transition into elevated-temperature behavior.
Reduced risk of distortion during a fire event, since locked-in residual stresses are already low.

These characteristics are recognized by EN 1993-1-2 (Eurocode 3, Part 1-2: Structural fire design), the European standard that provides the rules for designing steel structures for accidental fire exposure [$TRAE_REF](https://standards.iteh.ai/catalog/standards/cen/11d3ae10-a9fa-4bb4-89af-d06d4cccdcb5/en-1993-1-2-2024).

Critical Temperature and Strength Reduction

EN 1993-1-2 uses reduction factors to describe how the yield strength and stiffness of structural steel degrade with temperature. The "critical temperature" is the steel temperature at which a member can no longer carry the applied load with the required safety factor.

For typical EN 10210 grades (S235, S275, S355), the behavior is broadly the same as for other hot-rolled carbon steels. At about 400 °C, the steel still retains around 100% of its ambient yield strength. Past 500 °C, strength drops off progressively. By 600 °C, only about 60% of the ambient yield strength remains, and by 700 °C the figure falls to roughly 30%.

Two practical takeaways:

A 30-minute (R30) fire rating is achievable for many EN 10210 sections without any applied fire protection, depending on the load ratio.
Higher ratings (R60, R90, R120) almost always require either thicker sections, lower utilization at ambient, or a fire-protection system.

The Section Factor: Why Hollow Shapes Heat Up Fast

The section factor Am/V (the ratio of the exposed surface area to the volume of steel) is the single most important geometric input for an unprotected steel member in fire. Hollow sections generally have lower Am/V values than open sections of equivalent mass, which is a structural advantage in fire because less steel surface is exposed per unit of mass.

However, the inner surface of a hollow section is sealed off from the fire, so it does not contribute to heating. In practice, this means an EN 10210 circular or square hollow section can sometimes meet a 30-minute rating where an open section of similar weight cannot.

A typical relationship between section factor and required protection thickness for a cellulosic fire is shown below, based on EN 1993-1-2 and common manufacturer data for protected hollow sections:

Section Factor Am/V (m⁻¹)	R60 Thickness	R90 Thickness	R120 Thickness
≤ 100	12 mm	20 mm	30 mm
100 – 150	18 mm	28 mm	42 mm
150 – 200	25 mm	38 mm	—

These are indicative values for protected hollow sections; actual design thicknesses must be confirmed against the specific product's fire-test assessment or manufacturer's loading tables.

EN 10210 vs. EN 10219 in a Fire

A common question is whether EN 10210 sections perform better in fire than cold-formed EN 10219 sections of the same grade and weight. The short answer is that, for ambient design properties, EN 10210 sections have a slight edge: an S355 grade under EN 10210 guarantees a minimum 355 MPa yield, while under EN 10219 the same grade name corresponds to 345 MPa because the grade refers to the feedstock rather than the finished section [$TRAE_REF](https://www.lefinsteel.net/news/en-10210-vs-en-10219-which-european-standar-85574376.html).

In a fire, that 10 MPa advantage is not usually the deciding factor. What matters more is the consistency of mechanical properties through the section. Because EN 10210 sections are hot-finished above 580 °C, their strength and stiffness degrade more predictably as the section heats uniformly. Cold-formed sections can have localized property variations around the corners, where cold work has hardened the steel, which can complicate fire analysis.

For fire-critical structures (high-rise buildings, offshore platforms, escape-route structures in public buildings), this consistency is a real benefit and is one of the reasons EN 10210 is the default specification.

Fire Protection Options for EN 10210 Hollow Sections

Where the required fire rating exceeds the inherent capacity of the bare steel, three protection routes are commonly used on EN 10210 sections:

Intumescent Coatings

Thin-film intumescent paint expands into a thick insulating ｃｈａｒ when exposed to heat, slowing the temperature rise in the steel. These coatings are widely used on exposed structural steel because they preserve the architectural appearance of the section [$TRAE_REF](https://steeltubeinstitute.org/resources/keeping-your-cool-how-to-get-started-with-hss-fire-ratings/). Thicknesses are typically specified from the coating manufacturer's load-specific tables.

Spray-Applied Cementitious Fireproofing

Spray-applied fire-resistive material (SFRM) is the traditional option for concealed steel. It is economical and provides reliable insulation, but it adds significant thickness and weight and is not suited to architecturally exposed steel [$TRAE_REF](https://bahlfireproofing.com/intumescent-vs-cementitious-fireproofing/).

Encapsulation with Board Systems

Gypsum or calcium-silicate board enclosures are common in commercial buildings where the section is hidden behind services. They are clean to install and easy to inspect, but they consume floor space.

A Practical Specification Checklist

When EN 10210 sections are being specified for a project with fire-design requirements, the following points should be locked in before procurement:

State the standard and the grade explicitly – "EN 10210 S355J2H" is unambiguous; "S355J2H" alone is not.
Confirm the required fire-resistance rating (R30, R60, R90, R120) from the applicable building code or project specification.
Decide the protection strategy early – intumescent, SFRM, or board. The choice affects member sizing, section factor, and cost.
Calculate the section factor Am/V for each member used in fire analysis, since it directly drives protection thickness.
Request a mill test certificate (MTC / 3.1 certificate) confirming the heat number, grade, and mechanical properties. EN 10210 suppliers should be able to provide this as standard.
Consider CE marking – both EN 10210 and EN 10219 are harmonized under the EU Construction Products Regulation, and CE-marked sections come with a Declaration of Performance that includes the relevant fire classification.

Sourcing EN 10210 Sections for Fire-Critical Projects

A reliable EN 10210 supply is the foundation of a defensible fire design. Look for a manufacturer that can deliver sections in S235JRH, S275J2H, and S355J2H grades, in circular, square, rectangular, and elliptical forms, with full traceability and mill-certified mechanical properties. EZ Steel Industrial supplies EN 10210 hot-finished hollow sections in these grades, with optional in-house cutting, finishing, and bundled project supply for EPC and structural contractors.

For project-specific support, including section-factor calculations, grade selection, and coordination with your fire-protection subcontractor, reach out through the EZ Steel Industrial contact page or send your inquiry to export@ezsteelpipe.com.

Key Takeaways

EN 10210 hot-finished sections have uniform properties and low residual stress, which makes their fire behavior more predictable than cold-formed equivalents.
Fire design of EN 10210 sections follows EN 1993-1-2, using critical temperature and section factor Am/V as the main inputs.
Unprotected EN 10210 sections can often meet R30 ratings; higher ratings typically require fire protection (intumescent, SFRM, or board).
Always specify the full standard + grade combination (for example, EN 10210 S355J2H) and request a mill test certificate for traceability.

A well-written EN 10210 specification, paired with the right fire-protection strategy, gives structural engineers a robust path to compliant, cost-effective fire design for buildings, bridges, and offshore structures.