April 19, 2007

Keeping an airborne threat at bay

  • Proper construction and maintenance procedures can prevent the spread of deadly spores
    Coffman Engineers


    More and more, the modern hospital is the site of continuing overhaul and remodel.

    The presence of construction activity in the midst of patient care exacerbates the dangers for a critical patient. The number of people who die annually from hospital-acquired infections, in particular aspergillus, is believed to be larger than the number who die from AIDS, breast cancer or automobile accidents in this country.

    Aspergillus designates a range of fungal spores that grow where moisture is present, but can live for long periods (days, weeks, even months) in a completely dry environment. These spores are carried by dust particles, and can travel airborne for long periods.

    They typically do not affect healthy adults, but can cause illness and even death to adults who are weakened by surgery or have compromised immune systems. Hence, the control of aspergillus (as-per-JIH-lus) is a serious concern in hospitals.

    Leaks and drafts

    Image courtesy of Coffman Engineers
    Airborne fungal spores can sicken or kill adults who are weakened by surgery or have compromised immune systems. Surrounding work zones with air-movement barriers can help prevent their spread.

    Areas of the hospital where moisture creates a growing environment for aspergillus are numerous and often difficult to monitor and correct.

    Hospitals require numerous complex piping systems distributed throughout the building. Small leaks are not uncommon, and these leaks often occur in parts of the building that are difficult to observe, such as above ceilings or in wall cavities.

    A small leak can, over time, produce a lot of damage to the building fabric before being noticed and corrected. During this time, a flourishing colony of aspergillus can be produced.

    Cut off from moving air, the spores will remain contained. Once lofted into the air by drafts or thermal currents, the aspergillus will disperse over a wide area.

    Events that can expose these colonies of aspergillus to drafts and thermal currents appear benign, and they often consist of simple maintenance routines.

    Examples include a plumber running a short branch water line through a wall to a new plumbing fixture; an engineer removing ceiling tile to examine ductwork routing in the ceiling space; or a technician routing new data cable through the ceiling space and down in a wall to a desk.

    Not all such exposure events are caused by humans. A roof leak may cause moisture to collect on the ceiling below the leak, and aspergillus can grow at this moist ceiling surface. When the surface dries, the spores can be moved by drafts in the ceiling cavity to a different location or fall through joints in the ceiling to the occupied space below.

    Controlling air flow

    Can something be done to contain the aspergillus? Yes.

    Today, awareness of aspergillus has led maintenance staff to adopt new procedures that help contain aspergillus spores. Such procedures require surrounding the proposed work area with a barrier to the movement of air. On small projects a plastic sheet is typically used, but for larger, more elaborate projects, a temporary wall may be created.

    Progressively more sophisticated actions are being taken to plan for dust control during construction projects, both inside and, more recently, outside of the construction zone, including the following:

    • The area within the construction zone is maintained at negative pressure using exhaust fans. This draws air from the surrounding space into the construction zone, thus helping to minimize the flow of dust from the construction zone back out into neighboring areas of the hospital.

    The exhaust air is passed through filters and then discharged outside at a point where it will not be drawn back into the building through air intakes or open windows or doors. In addition, monitors are installed to assure that the pressure in the construction zone remains negative, with alarms that signal in the event negative pressurization is lost.

    Vestibules are required, with two sets of doors. With one door always closed, the other door can be opened without breaching the barrier and losing the negative pressure.

    • In the areas surrounding or adjacent to the construction zone, there is new awareness of the importance of maintaining the pressure differentials and airflow volumes that existed prior to construction.

    The public is not generally aware of the role that pressure differentials play in helping to control the spread of infectious agents within the hospital.

    In order to keep “clean” areas of the hospital maintained, positive air pressure is used with the resulting flow of air out from the “clean” space to the surrounding spaces. This helps prevent the flow of dust and germs from “dirty” areas into “clean” areas.

    “Dirty” areas of the hospital (soiled utility rooms, toilets, janitor’s closets) are maintained as negative pressure areas so that air flows into the “dirty” space from the surrounding spaces. This prevents dust and germs from flowing out of the “dirty” area into cleaner, surrounding areas.

    Ensuring proper ventilation

    When hospital construction requires interruption to the air distribution system, the pressure differentials and air volumes of adjacent spaces are often disrupted, with the loss of infection control and comfort conditioning that may be entailed.

    It is now standard practice to review all proposed construction barriers at the state and local level. While this review has always been related to life-safety issues, such as exiting and maintenance of fire barriers, the new role of this review is to establish that the interruptions to the local air distribution system will be properly addressed, both during construction and at the completion of construction, and that the construction zone ventilation itself will be properly done.

    The ongoing efforts to improve construction-related airborne infection control have created more complex systems. While they have raised the cost of health care, it is believed by the medical community to be important in reducing infections and improving patient care. The result is an increasing need for dedicated, well-trained maintenance staff.

    The proliferation of lawsuits connected with hospital-acquired infections has brought new appreciation on the part of hospital administration for the importance of their physical plant and those who operate and maintain it.

    Robert E. Rosenbaum is a senior project manager in the mechanical engineering department at Coffman Engineers, a multidisciplined engineering firm.

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