Isolation room project described

An initial overview of isolation room design requirements identified the criteria defined initially in HBN 27 (1993), through HBN 57 (2003), to NI/RACCDC/HE guidance (2004) and HBN 04-01 (2006).

Matthew Day explained that, ‘essentially HBNs 27 and 57 set forth the same premise – of a room provided with a lobby, and balanced supply and extract ventilation to both, with around six airchanges to the room, and 20 to the lobby, based on best practice and assumed scrub/gowning times of circa three minutes, resulting in a complete air change in the lobby during the transition between the room and corridor’. He added: “No pressure differentials were established or monitored, and there was no indication, as such, that ‘isolation’ was being achieved.”

With the advent of SARS in Asia, work was commissioned in Northern Ireland and England to develop enhanced isolation rooms designs, with the NI RACCDC/HE standard appearing in 2004, defining the criteria for isolation in engineering, building, and clinical terms, and identifying different room types. Essentially, Matthew Day explained, the model introduced pressure differentials across each room interface of 15 Pa, and a room air change rate of 12 to 15. A full-scale mock-up was constructed at the Belfast Royal Hospital.

The ‘slightly later’ HBN 04-01 was developed following extensive worldwide research, and in conjunction with the BRE, which built a full-scale mock-up to facilitate extensive testing, and undertook CFD modelling to predict the efficacy of the prescribed airflow patterns to achieve changeover of room air volume. Matthew Day said: “Like the NI standard, the HBN defined pressure and air change differentials, although these were 10 Pa across room interfaces, and 10 air changes to the room itself.The principal difference, however, was that in the HBN no air was either supplied or extracted direct from the room; instead supply air was introduced into the gowning lobby and transferred to the room via a pressure stabiliser, before being extracted from the en suite via an air transfer grille. Both the NI and HBN models, however, required dedicated air-handling units and extract fans.”

The speaker explained that the City Hospitals Sunderland NHS Foundation Trust assembled a design team to deliver a new modular ward block with three 40-bed wards (one renal), an 18 bed ICCU, and 16 isolation rooms (four per floor). The team comprised project manager/ quantity surveyor, and CDM, DKP; architects, HDP; structural engineers, SFS&P, and M&E consulting engineers, DSSR. The innovative ICCU layout included 13 ICCU bedrooms with switchable glazed walls to three sides, four ‘switchable pressure’ isolation rooms, a central clinical corridor, and a ‘dirty’ corridor for non-clinical access to empty ‘pass through’ waste bins.

Diagrams were developed to illustrate the isolation principles to be delivered in each mode of isolation room operation.

In keeping with HBN 04-01, the lobby/ room/en suite arrangements were kept ‘pressure neutral’ to the clinical corridor, with pressure differentials and airflows ‘swung’ within the suite, by designing the ductwork to keep pressure paths equal, and motorised dampers to divert supply/ extract air provision between the isolation room and the lobby.

Mathew Day explained: “Potentially 16 isolation rooms could have required 16 air-handling units, or, at best, four AHUs, to comply with HBN 04-01. However a solution was developed requiring only two air-handling units, each rated at 100%, and running normally at 50% in parallel, so that, in the event of a failure or maintenance requirement, the affected AHU can be taken offline, and the other ramped up to 100%, to ensure continued operation of all 16 rooms.

“Clearly, with ‘switchable’ pressure isolation rooms, there is an opportunity for mis-application of a particular pressure regime inappropriate for a particular patient. The switching function is thus keycontrolled by infection control staff, with indication provided both locally at the room, and at the staff base, via a simple ‘traffic light ‘system.”

Nothing new under the sun

Matthew Day added that during an April 2013 visit to the Children’s Infectious Disease Hospital in Simferopol in the Crimea, he saw an isolation room arrangement (see Fig.1) designed and built in the early 1970s, with a central clinical corridor and external family access, thereby separating clinical and non-clinical/family access/egress via lobbies, with clinical washandbasins in the room and lobby, and UV light utilised for bacterial control. He said: “This facility demonstrated many of the isolation and infection control principles developed through our ‘latest’ guidance and innovative designs.”