Each type of construction product has its own way of expressing fire performance. Through this series, we explain how to read and interpret classification codes according to the relevant European standards.
Part 1 – Fire Resistance Classification of Ventilation Ducts
Applicable standards
- Testing: EN 1366-1:2014+A1:2020
- Classification: EN 13501-3:2025
- Extended application of test results: EN 15882-1:2011+A1:2017
| Designation | Meaning | Note |
|---|---|---|
| E | Integrity | |
| EI | Insulation | |
| ttt | Classification period | 15, 20, 30, 45, 60, 90, 120, 180, 240 minutes |
| ve | Vertical orientation of duct | |
| ho | Horizontal orientation of duct | |
| (o→i) | Fire outside duct | Duct A |
| (i→o) | Fire inside duct | Duct B |
| (i↔o) | Fire from inside to outside duct and vice versa |
|
| S | Smoke leakage | Valid for duct A only |
How to read the classification of ventilation ducts
The fire resistance classification of ventilation ducts according to EN 13501-3 defines how long a duct maintains its integrity (E) and, where applicable, its insulation (I) during fire exposure.
Each classification code includes several elements describing the test conditions:
- fire resistance time in minutes (e.g. 45, 90, 120);
- duct orientation – vertical (ve) or horizontal (ho);
- direction of fire exposure – from outside (o→i), from inside (i→o), or from both sides (i↔o);
- and possibly enhanced leakage performance (S), which applies only to duct type A.
Examples
EI 45 (ho o→i) S
This represents the classification of a horizontal duct exposed to fire from outside. The integrity, insulation and smoke leakage criteria are satisfied for a classification period of 45 minutes.
EI 30 (ve ho i↔o)
This indicates a ventilation duct capable of satisfying the integrity and insulation criteria for 30 minutes, from inside to outside and vice versa, in both vertical and horizontal applications.
