Aspirating smoke detector sensitivity decides how early the system raises an alarm. A higher sensitivity finds smoke sooner, but it also needs a cleaner room and a good design.
In this guide, we explain the sensitivity classes of EN 54-20, the alarm levels inside the detector and how to pick the right setting. We keep the language simple, so non-specialists can follow it.
What does aspirating smoke detector sensitivity mean?
Sensitivity is the smallest amount of smoke that makes the detector react. In an aspirating system, the detector measures the density of smoke in the air that arrives through the pipes. The lower the smoke level that triggers an alarm, the higher the sensitivity.
Because the air from many holes is mixed, the system also has a limit on how many holes it can serve at each sensitivity. This is why the class matters.
EN 54-20 classes A, B and C
The European standard EN 54-20 defines three classes. Class A is the most sensitive, then B, then C. Each class also limits the number of sampling holes.
| Classe | Sensibilidade | Utilização típica | ModuLaser holes per detector module |
|---|---|---|---|
| A | Very high | Critical areas such as data centres and clean rooms | Up to 20 |
| B | High | Enhanced protection of important areas | Up to 40 |
| C | Normal | General protection, like a good point detector grid | Até 50 |
Read the full detail in our guide to EN 54-20 Class A, B and C.
Alarm levels inside the detector
The sensitivity class sets the ability of the system. Also, the alarm levels set what happens as the smoke grows. The ModuLaser and MiniLaser offer four alarm levels. A low level can start a warning, while the higher levels can raise the fire alarm.
This staged approach gives staff time to react. For example, they can check a server rack at the first level before the fire alarm starts.
How to choose the right aspirating smoke detector sensitivity
Match the setting to the risk and to the room.
- Clean and critical: choose a very sensitive setting, such as in a data centre.
- Dusty or busy: use a lower sensitivity or longer delays, because dust can look like smoke.
- Strong airflow: smoke is diluted, so a sensitive system is more important. See cleanroom fire detection.
- Unusual conditions: cold, humid or high rooms need a design check from the maker.
Products and their sensitivity
The ModuLaser and the MiniLaser both support Classes A, B and C of EN 54-20. Also, MiniLaser offers 10, 20 or 35 sampling holes for the three classes. For setting the levels in practice, see our guide on aspirating detector false alarms.
Retiradas de chaves
- EN 54-20 defines Class A, B and C, from the highest to the normal sensitivity.
- Each class also limits the number of sampling holes per detector.
- Four alarm levels give staff time to react before the fire alarm starts.
- Match the sensitivity to the room: high for clean and critical areas, lower for dusty ones.
Perguntas mais frequentes
What is the most sensitive class of aspirating smoke detector?
Class A of EN 54-20 is the most sensitive, followed by Class B and Class C.
Is higher sensitivity always better?
No. A very sensitive setting in a dusty room can cause nuisance alarms. Choose the sensitivity that fits the risk and the room.
How many alarm levels does the ModuLaser have?
The ModuLaser and the MiniLaser offer four alarm levels with ClassiFire intelligence.
Can I change the sensitivity later?
Yes. The settings can be adjusted at the detector or with the software, but a change must be checked and recorded.
For an overview, read Aspirating Smoke Detector: How It Works and When to Use One and our aspirating smoke detection systems page.