Mineral wool, glass-fibre mats and membranes, gypsum, cement boards and many inorganic coatings are sold on one claim: Euroclass A1 or A2. Behind that claim, in almost every case, is EN ISO 1182 — the non-combustibility test carried out in a small vertical tube furnace.
The current edition is ISO 1182:2020 (EN ISO 1182:2020), which replaced the 2010 edition. Among other changes, the 2020 edition introduced a second furnace thermocouple, so that the furnace temperature is taken as an average of two readings rather than one.
This article is for manufacturers who run the test in-house for development and production control, and who need their in-house numbers to agree with the notified laboratory's.
What the test does
A cylindrical specimen, nominally 45 mm in diameter and 50 mm high, is lowered into a vertical tube furnace stabilised at around 750 °C. Thermocouples record the furnace temperature and, in addition, the temperature at the specimen surface and specimen centre. The operator watches for flaming. The specimen is weighed before and after.
Three results come out of each specimen:
- ΔT — the rise in furnace temperature caused by the specimen;
- Δm — mass loss, as a percentage of the original mass;
- tf — duration of sustained flaming.
Five specimens are tested, and the classification criteria are applied to the averages.
The EN 13501-1 criteria
| Criterion (average of 5) | Class A1 | Class A2 |
|---|---|---|
| Furnace temperature rise ΔT | ≤ 30 °C | ≤ 50 °C |
| Mass loss Δm | ≤ 50 % | ≤ 50 % |
| Sustained flaming tf | 0 s (none) | ≤ 20 s |
Two points are routinely missed:
- A1 is never decided by EN ISO 1182 alone. A1 also requires the gross heat of combustion test, EN ISO 1716, on the product and its components.
- **A2 can be reached via EN ISO 1182 or EN ISO 1716**, but for most products it also requires the single burning item test (EN 13823). An EN ISO 1182 result inside the A2 limits is necessary, not sufficient.
The same apparatus is used under the IMO Fire Test Procedures Code for marine materials, with different criteria — including a limit on the surface thermocouple rise and on flaming duration. A result evaluated against EN 13501-1 cannot simply be relabelled as an IMO result.
Error 1: inserting the specimen before the furnace has settled
The method requires the furnace to be stable at its set temperature before the specimen goes in. A furnace that is still drifting adds or subtracts degrees from ΔT — and the A1 limit is only 30 °C. Log the furnace temperature continuously and do not insert until the stability condition in the standard is met. A recorder with a short logging interval makes the drift visible; our furnace logs each of its four thermocouples every 0.5 s for exactly this reason.
Error 2: thermocouples that have aged
Type K thermocouples drift after repeated cycling at high temperature, and the furnace thermocouples are the measurement on which the classification rests. Keep a record of hours in service, check them against a reference on a fixed schedule, and replace them before drift becomes visible in results. The 2020 edition's two furnace thermocouples help: a growing difference between them is an early warning.
Error 3: specimens that do not represent the product
The specimen must be representative of the product as placed on the market — including binders, facings, coatings and pigments in their real proportions. Typical problems:
- cutting from the edge of a board, where density differs;
- removing a thin facing because it is awkward to cut;
- building up thin products to the specimen height in a way the standard does not describe.
Follow the specimen preparation clause exactly for your product type. Mineral wool, cast products and thin layers each have their own route.
Error 4: weighing at the wrong moment
Mass loss is calculated from the original mass and the mass after the specimen has cooled. Specimens should be conditioned before testing as the method requires, and weighed on a balance appropriate to the specimen mass. A hot specimen on a balance gives a wrong reading through convection; a specimen that has picked up moisture before the first weighing shows an inflated loss.
Error 5: missing short flames
For A1, any sustained flaming fails. Short flames inside the tube are easy to miss. Use the viewing mirror, keep the area around the furnace dim, and assign one person to watch for flaming throughout the test rather than combining it with other jobs.
Error 6: draughts around the furnace
The furnace sits in open air with a stabilising cone and draft screen. Ventilation, open doors and people walking past change the airflow through the tube and therefore the temperatures. Place the furnace away from extraction outlets and doors, and keep the screen in place.
Making in-house and external results agree
- Use the same edition of the standard as the external laboratory.
- Calibrate the furnace temperature profile as the standard describes, and keep the record.
- Prepare specimens from the same production lot as the samples sent out.
- Compare not only pass/fail but the individual ΔT, Δm and tf values. A systematic offset in ΔT usually points to thermocouples or stability, not to the product.
Report checklist
- Edition of EN ISO 1182 used.
- Individual and average ΔT, Δm and tf for all five specimens.
- Specimen preparation route and product layers included.
- Furnace stability and calibration records for the test day.
- Which classification standard the criteria were taken from.
Our EN ISO 1182 non-combustibility furnace, with four Class 1 type K thermocouples and PC software, is built in our own workshop in Istanbul for R&D and internal quality control. It is a natural pair with an oxygen bomb calorimeter for EN ISO 1716; see the ISO 1182 page.