Protective Air Enclosures in Health Buildings

Over the last 20 years there has been a substantial development in the engineering technology for providing protective air enclosures for different purposes. These include the following.

Health building laboratories probably have the widest range of hazards of any technological installation of similar size because, apart from the usual range of laboratory hazards of fire, gas cylinders, acids, etc., they pose distinct problems in the handling of dangerous aerosols or vapours which arise from incidence of bacteria and viruses, of dangerous chemicals (carcinogenic, explosive, combustible, corrosive) and of radioactive substances. In a way it is fortunate that the usual hospital laboratory does not carry these hazards at the highest levels. Thus bacterial and virus problems are not usually as serious as they are at a microbiological research station, except where special infectious nursing arrangements exist; the chemicals are not so seriously hazardous as are met in some chemical factories and the level of radioactivity handled and the way it is handled do not present the hazards of, say, a nuclear fuel processing plant.

Some elements occur and recur in the design of protective air enclosures whatever the design or purpose to which it is to be put. Among these are high efficiency filtration, laminar flow and air flow control. A general account of these principles is given at this stage so that the use of these terms will be more fully understood when the description of various air enclosures is considered in subsequent chapters.

The hazards that can be encountered in hospital laboratories have been discussed in chapter 2, as have the manipulations in the hospital laboratory which need protective air conditions. The types of protective air enclosure that are available to deal successfully with these hazards — fume cupboards, safety cabinets, laminar flow cabinets and the like — are many and varied. A good deal of confusion exists regarding the different types, their uses and deficiencies, which makes selection by the design engineer, maintenance by the hospital engineer and proper use by the hospital technician difficult.

The local air enclosures whose main characteristics and general usage were outlined in chapter 4 are considered in further detail in this chapter. Design features are discussed in relation to the nature of the performance characteristics required to enable them to work satisfactorily within the health building environment. It is not intended to involve detailed mechanical design or detailed specifications although some references are given which will help the reader towards a more detailed understanding of the engineering.

The satisfactory operation of fume cupboards or other laboratory enclosures in relation to maintaining an adequate air flow at all times cannot be ensured unless a number of ancillary devices are taken into account. Not all possible such devices are required for every installation but thought should be given before any of them are excluded: the intended use will dictate whether any can be omitted.

As we have seen, laboratories in health buildings are sources of many toxic hazards. Even if protective air enclosures are used for those operations which give rise to particular hazards or obnoxious materials, laboratories as a whole still contain indefinite hazards, smells and fumes, and it is most desirable that some degree of ventilation be arranged.

As we have seen, protective air enclosures are mostly used for protection against hazardous materials being inhaled by operatives, and in all these applications the advantages obtained from carefully trapping the dangerous materials into a confined air stream are of doubtful value if that air stream is not extracted and dispersed so that it cannot be driven back into the laboratory itself, cannot reenter the hospital at any point and cannot disperse in a manner that would contaminate adjacent buildings. We have seen in chapter 6 how a number of ancillaries to air enclosures should be considered to assist in developing a satisfactory direct extraction. Problems now arise relating to how to engineer a complete ducting and dispersal system from the enclosure to a point where it is sufficiently dispersed so as to cause no harm.

While general design aspects of protective air enclosures in hospital laboratories have been considered in detail in chapters 4 to 9, it is now desirable to complete this account by reference to how such protective air enclosures should be operated and tested, with some reference to the problems of maintenance in such conditions of potential hazard.

The protective air enclosure that has received most attention, particularly in the last twenty years, in hospitals, is the operating theatre. This differs, however, from the hospital laboratory enclosure in that the work to be done is generally performed within the enclosure and the objective is to keep the air clean, particularly in the region of the patient being operated on, but also in such areas associated with the operation as may contribute to infective micro-organisms entering the region of the patient. The problem is therefore to try to ensure that infective micro-organisms or other harmful particles do not reach the surgical wound site. These undesirable particles can be present in the air of the room or on personnel or articles that are in the operating room or on the patient himself. Many techniques and operating methods have been developed by different surgeons for dealing with the latter, but the engineer is mainly concerned with the problem of keeping the air clean around the operating site, whatever the source of the undesirable particles within his control.

Concurrently with the development of protective air enclosures for surgical operating facilities there has been a development in nursing facilities in two main areas in which air cleanliness has been particularly relevant. The first is where the patient has an infectious disease and it is necessary to try to ensure that airborne micro-organisms do not escape from the region around the patient to contaminate other people. This requires what is known as ‘source isolation’ or ‘containment isolation’ and covers the nursing of patients with highly communicable diseases such as pneumonia, infected burns, plague and rabies, enteric diseases, wound infections, skin infections and respiratory infections, [1] smallpox, diptheria, typhoid, tuberculosis, meningitis, hepatitis, measles, etc. [2] The degree of risk here is variable and therefore the quality of protective air enclosure relates to the risk.

The preceding chapters have described the general features and principles of protective air enclosures as used in the main areas of hospitals where air protective measures have been developed. In the hospital as a whole, as distinct from the hospital laboratory or operating or nursing rooms, those areas where attention is given to air as a protective medium are: wound dressing rooms, intensive-care wards, etc., pharmacies, and post-mortem facilities.