A question that keeps coming up on smoke shaft projects: do the damper blades need to be insulated? The honest answer is “it depends”, and what it depends on is written in the damper’s classification string. Once you can read that string, the insulation question, and most other damper specification questions, answer themselves.
This article decodes the classification system for smoke control dampers: what E, S and I each prove, what the rest of the string means, the difference between single-compartment and multi-compartment dampers, and what BS 9991:2024 changed for residential specifications.
The Standards That Apply (and One That Doesn’t)
Smoke control dampers are fire safety products. They sit under Part B of the Building Regulations and the building’s fire strategy, with BS 9991:2024 giving the design guidance for residential buildings and BS 9999 for non-residential. They have nothing to do with Part F, which covers everyday ventilation for indoor air quality. If a specification justifies a smoke shaft damper by reference to Part F, that’s a flag worth raising.
Three European standards do the work:
- BS EN 12101-8 is the product standard a smoke control damper is certified against.
- BS EN 1366-10 is the fire resistance test method. Multi-compartment dampers are additionally tested to BS EN 1366-2, the same test method used for fire dampers.
- BS EN 13501-4 turns the test results into the classification string you see on the Declaration of Performance.
This framework is separate from the one for fire dampers (BS EN 15650, tested to BS EN 1366-2, classified to BS EN 13501-3). If you’re not sure which product a location needs, start with Smoke Damper vs Fire Damper: What is the Difference?
What E, S and I Actually Mean
A smoke control damper is classified against up to three performance criteria, each proven by test.
E is integrity. The damper stays in one piece and blocks the passage of flames and hot gases for the declared duration. Integrity also carries a backstop leakage limit: even a damper with no S classification must not leak more than 360 m³ per hour per m² of damper face area during the fire test.
S is smoke leakage. A damper with an S classification leaked no more than 200 m³ per hour per m² of face area, proven twice: once at ambient temperature, and again during the fire resistance test. The number after the S is the pressure class. S1000 means the ambient leakage test ran at 1000 Pa underpressure (DoPs often quote it as -1000 Pa); during the fire test the pressure is reduced (150 Pa for the 500 Pa class, 300 Pa for the 1000 Pa class, 500 Pa for the 1500 Pa class). The leakage limit is the same 200 m³/(h·m²) in every class; what changes is the pressure the damper proved it at.
I is insulation. The blade and casing limit heat transfer to the non-fire side. The criterion fails if the unexposed face rises more than 140°C above ambient on average, or more than 180°C above ambient at any single point. Insulation is the only one of the three that is genuinely optional: plenty of correctly specified smoke control dampers carry no I rating at all.
Reading a Full Classification String
A real multi-compartment damper classification looks like this:
EI 120 (ved,hodw,i↔o) S1000 C10000 HOT 400/30 MAmulti
Broken into its parts:
| Element | Meaning |
|---|---|
| EI 120 | Integrity and insulation maintained for 120 minutes |
| ved,hodw | Tested orientations: ve = vertical, ho = horizontal; d = mounted on a duct, w = in a wall, dw = both |
| i↔o | Fire tested from both sides (i→o or o→i means one side only) |
| S1000 | Smoke leakage class, 1000 Pa ambient test pressure |
| C10000 | 10,000 operation cycles, the class for dampers also used for daily ventilation (C300 covers smoke-control-only duty; Cmod covers modulating dampers) |
| HOT 400/30 | Can still be driven open and closed at 400°C for 30 minutes |
| MA | Also proven for manual intervention (AA, automatic activation, is the usual class for dampers driven by the smoke control system) |
| multi | Approved for multi-compartment use |
Every element matters at specification time. A damper classified ved only has no test evidence for wall mounting. A damper classified i→o has only been tested with fire from one side, and a corridor damper can face fire from either side. The orientation and construction type on site must match the orientation and construction type on the certificate, or the test evidence doesn’t apply.
Single-Compartment vs Multi-Compartment Dampers
BS EN 12101-8 splits smoke control dampers into two categories, and the split decides most of the insulation question.
Single-compartment dampers serve one fire compartment only. They’re fire tested at a constant 600°C rather than on the standard time-temperature curve, and classified E600, so a typical string reads E600 120 (ved,i↔o) S1500 C10000 MAsingle. That 600°C test represents hot smoke, not a developed fire. A single-compartment damper is not tested to maintain compartmentation, and must never be installed where the damper penetrates a compartment wall or floor.
Multi-compartment dampers are the ones that may breach compartment boundaries: the damper on each floor of a smoke shaft, connecting a common corridor to a shaft that runs the height of the building, is the textbook case. These are tested on the standard fire curve to BS EN 1366-2 as well as BS EN 1366-10, and carry a conventional minutes rating (E or EI 60, 90, 120) with the “multi” suffix. The Smoke Control Association recommends that smoke shaft dampers should be multi-compartment smoke control dampers (“multi-zone” in the SCA’s white paper) CE/UKCA marked to BS EN 12101-8, because nothing else has test evidence for maintaining compartmentation in a shaft.
The rule of thumb: a multi-compartment damper may be used for a single-compartment job, but a single-compartment damper may never be used for a multi-compartment one.
A note on terminology: you’ll see “MCD” and “MSCD” on drawings and in catalogues, and different manufacturers mean different things by them. The standard’s own terms are single-compartment and multi-compartment smoke control damper. Spell it out, and check the DoP rather than the acronym.
So When Do the Blades Need to Be Insulated?
Here is the part specifiers argue about. Under the standard itself, insulation is optional even for multi-compartment dampers: an E 90 (vew,i↔o) S1000 C10000 AAmulti classification with no I is a perfectly valid one. So “multi-compartment” does not automatically mean “insulated”.
What decides it is the construction the damper sits in. If the damper is installed in a fire-resisting wall or floor that carries an insulation rating, and the fire strategy relies on that rating to protect the space on the other side, the damper must not become the weak point through which heat radiates. That’s when an EI classification is required, matched in minutes to the element it penetrates. If the strategy only needs the boundary to hold back flames and smoke, integrity without insulation can be sufficient.
BS 9991:2024 leaned firmly in one direction for residential buildings. It expects smoke control dampers to comply with BS EN 12101-8, achieve leakage class S1000, carry at least a C10000 operations classification, be tested from both sides in their installed orientation and construction type, and provide fire resistance equivalent to the compartment they’re installed in. Dampers are no longer treated as loose components; they’re expected to perform to the same standard as the fire-resisting elements they sit within. In practice that has made EI 120 S1000 C10000 multi the default specification for new residential smoke shafts, and it’s why several manufacturers launched insulated dampers specifically aimed at the 2024 revision. The 1000 Pa leakage pressure is itself a step up: many older products were certified at the 500 Pa class, and they don’t satisfy an S1000 specification. We’ve covered the wider revision in BS 9991:2024: What Changed.
Neither shortcut survives contact with a real project. “An ES damper is always fine” fails the moment the damper sits in a rated separating element that needs its insulation preserved. “EI is always needed” gold-plates single-compartment applications where the standard never asked for it. The fire strategy and the damper’s Declaration of Performance settle it, not a default.
Common Specification Mistakes
- A single-compartment damper in a smoke shaft. E600 products are cheaper, and they turn up in tenders for multi-compartment positions where they have no test evidence at all. Check for the “multi” suffix.
- Quoting a leakage class without its pressure. “Class S” means little on its own. S500 and S1000 are different products as far as BS 9991:2024 is concerned.
- Orientation and construction mismatch. A damper tested ved (vertical, duct-mounted) installed horizontally in a wall is outside its certification, however good the product.
- One-sided fire testing in a two-sided location. Corridor and shaft dampers can face fire from either direction. Look for i↔o.
- Reading the brochure instead of the DoP. The classification string on the Declaration of Performance is the only statement of performance that counts. If the string isn’t shown, ask for it.
Practical Takeaway
The classification string is the damper. E, the minutes, and the single/multi suffix tell you whether it can legally sit where you want to put it; S and its pressure class tell you whether it meets the leakage spec; I tells you whether the blades are insulated, and the construction it penetrates tells you whether they need to be. For residential work to BS 9991:2024, expect to specify EI-rated, S1000, C10000, multi-compartment dampers tested from both sides, and confirm every element of the string against the Declaration of Performance before the order goes in.
Further Reading
- Smoke Damper vs Fire Damper: What is the Difference?
- BS 9991:2024: What Changed
- Anatomy of a Smoke Control System
- Smoke ventilation glossary
Sources
Official guidance and standards referenced in this article:
- BS 9991:2024, BSI Knowledge
- Approved Document B (fire safety), GOV.UK
- Smoke Control Association
- CIBSE Journal CPD Module 155: Smoke control dampers
- Swegon: A Guide to Smoke Control Damper Classifications
Specifying Smoke Control Dampers?
We supply BS EN 12101-8 certified smoke control dampers alongside the smoke control panels and actuators that drive them, with UK stock in Poole and next-working-day despatch on most lines. Our technical team can check a damper classification against your fire strategy before you commit to it.
Call 01202 725 689 or email info@vent-trade.co.uk.
