Over Pressure Vents are usually overlooked or completely forgotten on Gas Fire Suppression Systems especially on older systems.
The basic premise of an Over Pressure Vent is to provide protection to a room where it is subject to positive or negative pressure during the discharge of a gas fire suppression system.
Where a gas fire suppression system has been fitted in a room such as Novec 1230, FM200 or Inert Gas (IG55, INERGEN, IG541 etc) then the room during a discharge will be subject to postive (all types) and negative pressures (FM200 and Novec 1230 only) to varying degrees.
An Over Pressure Vent will provide an outlet for this to fresh air and will only operate when the pressure is either +100bar or -100bar and they operate as a weighted blade and do not require any interfacing into the fire suppression system.
There are two versions of our Over Pressure Vents, Stand-a-Lone or Combined Extract-Over Pressure Vents. The Combined units allow you to satisfy both the Over Pressure part of the standards and the Extract part once the gas has been discharged into the room in one unit.
Please click Combined Extract-Over Pressure Vents to see the products available or if you know what you want then click shop to purchase directly from us.
How Do I Calculate the Free Vent Area?
Over Pressure Vents come in 5 different sizes but the size you need is based on the amount of gas, the room size and the type of construction and is then described by the size of the Free Vent Area (FVA) in m2. The FVA is calculated at the design stage of the Gas Fire Suppression System and will be available on the Flow Calculation document provided by your installer and will look like this:-
The above example shows the individual areas FVA (ceiling void, room and floor void) described in m2, add all numbers together to calculate the full size of the Free Vent Area, 0.029m2. This would mean you would need our MPV150 based on a wall strength of 250Pa.
How Do I Select The Wall Strength?
This the the most asked question as the calculation should be done by your building designer or architect but in our expereince it is rare that you will get to know.
As a quick and easy rule of thumb we suggest the following:-
| Room Material | Pressure (Pascals) | Pressure (Mbar) |
| Block | 250 | 2.5 |
| Timber | 500 | 5.0 |
| Glass | 100 | 1.0 |
If you are unsure or don’t have the necessary paperwork please contact us with the absolute basic details of Gas type and Quantity, Room Volume and Wall Construction Type and we will calculate this for you.
Please go to our Shop to select the vent you require.