Cascade ventilation systems are widely used in hospitals, particularly for the ventilation of operating theatres. They are also employed in Isolation Rooms, Pharmacies, CSSD's (Central Sterile Supplies Units) HSDU's (Hospital Sterilisation and Disinfection Units), and TSSU's (Theatre Sterile Supplies Units) and in some specialist wards.
Operating theatre suite ventilation is designed in accordance with Health Service standard HTM 03-01 which has replaced HTM 2025 from November 2007 for new build projects.
These standards require the use of Pressure Stabilisers to give accurate control of pressure between rooms.
The rationale behind the HTM is to protect rooms in descending order of sterility with a cascade pressure system that allows sterile air to flow from the most sterile to the dirtiest rooms in a series of pressure steps.
This works well while all the doors in the theatre suite are closed but cannot cope with open doors which defeat the pressure gradient. Thus the suite is also designed to allow for protection of individual key open doors with a sufficient velocity of air to "sweep away" bacteria and dust from sterile areas to dirty areas. Dual duty stabilisers are offered to meet the requirements for door protection.
Supply and extract air volumes are specified in the HTM to take account of air change rates, heat gains and door protection. Where heat gains are greater than indicated, e.g. in theatres with Ultra Clean Ventilation canopies, the theatre supply may need to be increased.
It is permissible and indeed normal, to use pressure stabilisers in all applications within the theatre, rather than using pressure relief valves that are indicated in the HTM 2025 for some applications, e.g. Prep - Theatre and Corridor - Dirty Utility. HTM 03 has now recognised this.
It is increasingly necessary to protect theatre suites against fire and smoke ingress and for these applications we offer a full range of fire and fire/smoke rated pressure stabilisers fire tested to BS 476 Part 22.
Other pressurised areas within hospitals
Sterile Supplies Units (SSD), also known as Hospital Sterilisation and Disinfection Units (HSDU) and Theatre Sterile Supplies Units (TSSU) use pressure stabilisers to provide an accurate cascade ventilation system, to maintain sterility. HBN 13 is the Health Service standard covering these areas.
Isolation rooms are designed to meet the requirements of HBN 4 for sterility and/or the spread of infection, using a pressurised lobby.
Pharmacies typically have sterile manufacturing areas which are pressurised.
The Aercon® LF range of Pressure stabilisers in standard, fire rated and smoke rated forms are ideal for all hospital applications.
The premium range Type W Air Pressure Control Valves should be considered for overseas applications where high humidity is likely to be encountered. The standard heavy duty polyester/epoxy coated carbon steel bodies offer excellent corrosion resistance and all Type W valves can be removed from their wall sleeves for cleaning purposes without the need for tools.
A free computer aided application and design service is available for hospital applications to meet the relevant Health Service standards.
To take advantage of this service, please forward a floor plan either by fax or email (in a pdf format) and we will be delighted to provide a set of calculations showing where every litre of air comes from and goes to and how it gets there. For operating theatres please state whether the Prep room is a Lay-up or a Sterile Pack Store and which HTM standard you are working to.