What is Positive Pressure Ventilation?
Positive Pressure Ventilation (PPV), also known as Positive Input Ventilation (PIV), is a technique used to prevent smoke movement into vertical escape routes so occupants can escape. PPV takes proven engineering principles and applies them to establish a means of escape in accordance with Approved Document B (ADB).
When a PPV fan is activated, the positive pressure created by the PPV fan pressurises the lobby and prevents the ingress of smoke to the vertical escape stairwell. Air from the escape route is blown into the protected lobby by the PPV unit, raising it to a higher pressure to prevent the ingress of smoke from a car park, bike or bin store fire into the lobby. Air flows from a higher pressure zone to a lower pressure zone through the gaps around the doorways, forcing the fire gases away.
Why We Ventilate
The PPV Unit, Lobby Pressurisation, has been designed to provide an alternative approach to the natural 0.4mý permanent ventilation within the basement or ground floor lobbies, where prescribed in the ADB.
Section 3.74 of Approved Document B1 identifies that where lobby ventilation is required for B1 means of escape to protect the stair, protection can be achieved by natural ventilation or mechanical smoke control.
Section 7.6 of the Smoke Control Association (SCA) guidance document on residential buildings 2015 provides additional guidance on how to meet the mechanical smoke control requirements using pressurisation. The BS9991:2015 references the SCA document as a source for further design guidance.
Fitted PPV systems
A Lobby Pressurisation unit contains duty and standby fans, duty as well as standby fire dampers, a smoke detector interface, a single-phase automatic electrical change-over switch and a volt-free contact to enable third-party monitoring.
The unit damper fits into a 0.3m x 0.8m structural opening within the compartment wall and can be positioned in any orientation if the fire damper remains within the compartment wall.
Positive Pressurisation Ventilation from Be Safe Direct
Innobuild UK is the leading distributor of the PPV unit to the market and can offer technical support to the installer to assist with installing the lobby pressurisation system.
Fix the PPV unit in the wall between the lobby and the stairwell, and it will prevent smoke from penetrating from the car park, bike or bin store when the doors are closed.
The system is operated by a smoke detector placed on the car park side of a lobby door or store, which will activate the PPV unit. The unit will then run until the smoke detector is reset. Make-up air for the PPV unit is required at the head of the stairwell and should be opened at the same time as the operation of the PPV unit.
As with any engineered system, the PPV concept should be agreed upon by the approving authorities before installation.
Benefits of PPV
PPV is a highly efficient, cost-effective engineering solution that provides multiple benefits, including occupying minimal space and removing the need for expensive fire shutters and CFD modelling that would otherwise be required.
PPV benefits include:
- Occupies minimum space.
- The expensive 0.4mý fire-rated duct (which should also be insulted, thereby increasing the cost further) does not need to be used.
- Low car park heights or stepping services around the fire duct are not a concern.
- The car park smoke clearance system does not need to be enhanced and can remain at ten air changes per hour or naturally ventilated in line with the ADB.
- A robust solution that keeps smoke leakage via the door cracks out of the staircase.
- Certificated fire damper to BSEN1366-2.
- ISO 5801:2008 single phase duty and standby fan.
- BS 5839 compliant smoke detector.
- A cost-effective solution is meeting the ADB & SCA recommendations for means of escape protection of the non-fire fighting stairway.
- The fan is capable of producing 0.5mü/s at a static pressure of 50 pa.
