Why you need to understand how a test is set up
Every figure in fire protection documents — “R 90”, “Group 4”, “2 h”, “60 minutes to UL 1709” — was obtained under specific test conditions. Without knowing those conditions, it is easy to apply a result where it is not valid: to a different section, a different fire exposure or a different coating system. Below we explain how fire tests are set up and how the main methods differ.
The test furnace
Fire tests are carried out in purpose-built furnaces fired by gas or liquid fuel:
- Vertical furnaces — for walls, partitions and doors, and also for columns, which are heated on all sides.
- Horizontal furnaces — for floors and beams; the specimen sits on top of the furnace and can be loaded.
- Small-scale furnaces — for testing individual elements and for preliminary tests.
The furnace temperature is measured with furnace thermocouples (plate thermometers in the European system), and the fuel supply is controlled so that the average temperature follows the specified curve within the permitted tolerances. For separating elements, the furnace overpressure is also controlled.
Fire exposure regimes
| Exposure | Where specified | Key features |
|---|---|---|
| Standard (cellulosic) | GOST 30247.0, EN 1363-1, ISO 834; in the US, ASTM E119 / UL 263 | T = 20 + 345·lg(8t + 1); 842 °C at 30 min, 945 °C at 60 min, 1049 °C at 120 min. The ASTM E119 curve is defined by a table and is close to it |
| Hydrocarbon (HC) | EN 1363-2, GOST R EN 1363-2-2014 | Quickly reaches a plateau of about 1100 °C |
| Rapid rise | UL 1709 | About 1093 °C (2000 °F) within 5 minutes, then a constant temperature |
| Hydrocarbon pool fire | ASTM E1529 | Specified source temperature and heat flux to the specimen |
| External fire | EN 1363-2 | Plateau of about 680 °C, for external elements |
| Jet fire | ISO 22899-1 | High heat flux plus the erosive action of a pressurised gas jet |
| Smouldering fire (slow heating) | EN 1363-2; annex to GOST R 53295 (Amendment No. 1) | Slow temperature rise; checks how intumescent coatings behave under slow heating |
The choice of exposure is determined by the fire scenario at the facility. For general-purpose buildings, the standard exposure is sufficient. For oil and gas processing units, tank farms and pump houses, hydrocarbon exposures are used, with jet fire added where a release of pressurised gas is possible.
Specimens
Structural steel
- GOST R 53295-2009: two identical specimens — columns of No. 20 I-section, 1700 mm high, unloaded and heated on four sides. The result is the time to 500 °C and a fire protection efficiency group (1–7). Amendment No. 1 added optional procedures for testing loaded columns and beams.
- EN 13381-4 and EN 13381-8: a series of specimens of different massivity and with different fire protection thicknesses, including loaded beams and unloaded columns. The result is a set of thickness tables as a function of section factor, design steel temperature and time.
- UL 263 / ASTM E119: a full-size assembly built to a specific design — columns, or beams with a floor — usually under load; for unloaded columns, a temperature criterion applies.
- UL 1709: columns of different massivity; the steel temperature is assessed under the rapid rise exposure.
Timber and cables
To assess the fire protection efficiency of treatments for timber to GOST R 53292-2009, small specimens are tested in the “ceramic tube” apparatus and their mass loss is determined. For cable coatings to GOST R 53311-2009, vertical cable bundles are tested for flame spread, and the effect of the coating on current-carrying capacity is determined. These are laboratory methods for assessing the properties of a fire protection product, not fire resistance tests of a structure.
Thermocouples and measurements
The steel temperature is measured with thermocouples attached to the steel beneath the coating. Thermocouples are placed on the web and flanges of the section at several cross-sections along the height or length, to capture uneven heating. In GOST R 53295, three thermocouples are fitted at the mid-height cross-section of the specimen — on the web of the I-section and on the inner faces of the flanges. European methods use considerably more thermocouples, because the results are used for statistical analysis and for deriving thickness tables.
In addition to temperature, the following are recorded:
- deflections and deformations of loaded specimens;
- coating behaviour: intumescence, cracking, detachment, collapse of the intumescent char;
- for separating elements — the temperature of the unexposed surface, and the occurrence of flaming and through-gaps.
Critical steel temperature
When heated, steel loses strength and stiffness; the temperature at which a member can no longer carry its design load is called the critical temperature. It depends on the load level, the support conditions and the type of member. Different systems approach it in different ways:
| Method | Criterion |
|---|---|
| GOST R 53295-2009 | A fixed 500 °C on the standard specimen |
| EN 13381-4/-8 | A range of design temperatures; the designer uses the value calculated for the member to EN 1993-1-2 |
| ASTM E119 (unloaded columns) | Average 538 °C (1000 °F); 649 °C (1200 °F) at any single point |
| UL 1709 | Average steel temperature of 538 °C (1000 °F) |
The practical consequence is that coating thicknesses from documents of different systems cannot be compared directly. A coating that achieved 60 minutes to 538 °C will give a shorter time to 500 °C on the same section.
Loaded and unloaded tests
An unloaded test is simpler and cheaper: it shows how the fire protection delays heating. Under load, however, the member deforms, and the intumescent layer may crack or detach. That is why European methods always include loaded specimens, and US assembly tests to UL 263 are generally carried out under load. In GOST R 53295 the unloaded test remains the main one, with loaded tests introduced as additional procedures.
What the result confirms
- The result applies only to the tested system: primer, fire protection layer, topcoat, reinforcing mesh and fixing method.
- Extension to other sections is permitted only under the rules of the method (thickness tables, extended application) and within the tested range.
- A fire test says nothing about durability. There are separate methods for that: EAD 350402-00-1106 (types X, Y, Z1, Z2), UL 2431, GOST R 71618-2024.
- The quality of site application is no less important than the test result: the dry film thickness must match the design, and the measurements must be documented.
The methods compared in one table
| Parameter | GOST R 53295 | EN 13381-8 | UL 263 / ASTM E119 | UL 1709 |
|---|---|---|---|---|
| Exposure | Standard | Standard (others possible to EN 1363-2) | Standard (ASTM E119) | Rapid rise, ~1093 °C |
| Specimens | 2 columns (I-section No. 20), unloaded | Series of beams and columns, some loaded | Full-size assembly | Columns of different massivity |
| Criterion | 500 °C | Range of design temperatures | Load-bearing capacity or temperature criteria | 538 °C average |
| Output | Group 1–7 | Thickness tables, class to EN 13501-2 | Assembly rating in hours, listing | Protection time for a given section and thickness |