Search

The phenomenon of boundary layer separation can be an important factor in determining a worker's exposure to toxic airborne pollutants. A conceptual model was developed to understand this phenomenon and to predict the average concentration in the reverse flow region downstream of a worker in a uniform freestream. Subsequently, the assumptions of this model were tested experimentally in wind tunnel studies. On the basis of these results, a revised model is presented and validated by using a tracer gas method. The revised model provides a reasonable estimate of the average concentration in the reverse flow region of the mannequin. Empirical models are presented that relate both the average concentration in the reverse flow region and the breathing zone concentration to the body dimensions and the freestream air velocity. Applications and limitations of the results are discussed.

Of 67 office workers 27 (40%) had documented tuberculin skin test conversions after an estimated 4-wk exposure to a coworker with cavitary tuberculosis. Worker complaints for more than 2 yr before the tuberculosis exposure prompted investigations of air quality in the building before and after the tuberculosis exposure. Carbon dioxide concentrations in many parts of the building were found to be above recommended levels, indicating suboptimal ventilation with outdoor air. We applied a mathematical model of airborne transmission to the data to assess the role of building ventilation and other transmission factors. We estimated that ventilation with outside air averaged about 15 feet 3/min (cfm) per occupant, the low end of acceptable ventilation, corresponding to CO2 levels of about 1,000 ppm. The model predicted that at 25 cfm per person 18 workers would have been infected (a 33% reduction) and at 35 cfm, a level considered optimal for comfort, that 13 workers would have been infected (an additional 19% reduction). Further increases in outdoor air ventilation would be impractical and would have resulted in progressively smaller increments in protection. According to the model, the index case added approximately 13 infectious doses (quanta) per hour (qph) to the office air during the exposure period, 10 times the average infectiousness reported in a large series of tuberculosis cases. Further modeling predicted that as infectiousness rises, ventilation would offer progressively less protection. We conclude that outdoor air ventilation that is inadequate for comfort may contribute to airborne infection but that the protection afforded to building occupants by ventilation above comfort levels may be inherently limited, especially when the level of exposure to infection is high.

Following the commissioning of a new suite of operating rooms air movement studies showed a flow of air away from the operating table towards the periphery of the room. Oral microbial flora dispersed by unmasked male and female volunteers standing one metre from the table failed to contaminate exposed settle plates placed on the table. The wearing of face masks by non-scrubbed staff working in an operating room with forced ventilation seems to be unnecessary.

Over a 5-month period, six patients in a general intensive therapy unit became colonized by Aspergillus species including Aspergillus fumigatus, and invasive infection occurred in at least two of them. Broncho-alveolar lavage was unhelpful in discriminating between infection and colonization. The source of infection was presumed to be disturbance of an accumulation of spores in fibrous insulation material above the perforated metal ceiling. Patients in such units without clearly identifiable defects of defence against infection may be at risk from aspergillosis. The risk can be reduced by improved hospital design, satisfactory ventilation and thorough regular cleaning of environmental surfaces.

Unfiltered outside air averages 1-15 pathogenic Aspergillus sp. colony forming units (cfu) m-3 although short-term fluctuations are substantial. Seasonal variation reflects increased spore prevalence during periods of greater availability of non-viable matter. In hospital, airborne spores reflect incomplete filtration, infiltration of outside air and shedding of adherent spores from introduced objects. In highly protected hospital areas supplied with air filtered at high efficiency, where aspergillus cfus may be as low as 0.01 cfu m-3, infiltration and shedding contribute a high fraction of ambient spores. Nosocomial aspergillosis occurs in linear proportion to the mean ambient hospital airborne spore content. An analysis presuming a steady-state dynamic equilibrium is imperfect because repeated sampling produces occasional high counts which violate a Poisson distribution. 'Mini-bursts' arise from disturbance of settled spores in dust, shedding spores from clothes or other subtle sources. These sources are best mitigated by increasing the air change rate. It is most important to protect bone marrow transplant patients, leukaemia and lymphoma patients undergoing intensive, potentially curative therapy. The optimal protective environments include high filtration efficiency, point-of-use filters, protection against infiltration and filter bypass, elimination of in-hospital sources, and high air change rates.

The primary purpose of a Sterile Services Department is the prevention of infection. A specific guide to Good Manufacturing Practice (GMP) has been published by the Institute of Sterile Service Management to assist managers to ensure that the final products are of the nature and quality intended. The testing and monitoring of machinery, such as autoclaves, has an obvious microbiological relevance but other practices, such as expire dates and presterilization of used items, are of dubious microbiological advantage and can act against the main aim. GMP recommendations on environmental controls have received disproportionate attention to the remainder of the document, particularly relating to packing rooms. The standard should not be seen as a primarily microbiological measure but as a sensible control to limit the ingress of unwanted dust, flies and people and provide basic ventilation. Tests indicate that the standard for particle counts can be achieved without structural alteration in some departments. Microbiological counts are similar to those within operating theatres and additional protective clothing is of no apparent advantage. Process failure is the main cause of risks to the patient, and other practices, although both relevant and important, should not be given a false microbiological significance as these can detract and distract attention from the main issue.

An experiment using 4,800 commercial broiler males (Ross x Ross) was conducted in 12 climatic chambers. Three levels of relative humidity (RH) (45, 40, to 80, and 75%) and two levels of internal air circulation (7.7 to 9.9 and 17.8 to 24.5 cm/s), with each level replicated and, therefore, forming a 3 x 2 x 2 factorial arrangement of treatments, arrangement of treatments, were imposed as the main effects. Broilers were group weighed and feed efficiencies calculated at 14, 28, and 42 days of age. Percentage dry matter of the litter and a subjective evaluation of general litter conditions (moisture and caking) were scored weekly, with the percentage nitrogen and total quality of litter produced in each chamber measured at the conclusion of the study. Ammonia levels were measured in each chamber every second day. A sample of birds (36) from each chamber was processed at 42 days and scored for litter spots and ammonia burns on the breast and for the incidence and severity of twisted legs, crooked toes, and infected and calloused hocks and foot pads. Mean body weight was significantly greater (32 g) at 42 days of age in birds exposed to 45% RH compared with the two higher regimens of RH. Both the incidence and severity of ammonia burns on the breast and infected foot pads were significantly higher with 75 versus 45% RH. Increases in RH significantly increased caking and litter moisture and reduced the percentage of dry matter and the percentage of nitrogen found in the litter. Ammonia levels were more variable but generally increased with increases in RH. The two levels of air movement within the chambers produced less influence on the environment than RH, although the scores for both litter moisture and caking were significantly lower with increased levels of internal air circulation.

"Sick building syndrome" (SBS) is one of the more colorful terms describing an increasingly common pattern of symptoms found among workers in modern office buildings. Core symptoms include lethargy, mucous membrane irritation, headache, eye irritation, and dry skin. To prompt a diagnosis of SBS, these otherwise common symptoms must be "excessively" reported and primarily "work-related." The World Health Organization now estimates that 30% of new or remodeled office buildings show signs of SBS, and that between 10% and 30% of the occupants of these buildings are affected by SBS. Despite such figures, SBS remains poorly researched and even more poorly understood. The following review provides the clinician an overview of SBS that will allow a more accurate differential diagnosis and will help to prevent the widespread suffering that can accrue when SBS is not quickly recognized.

The transmission of tuberculosis is a recognized risk in health-care settings. Several recent outbreaks of tuberculosis in health-care settings, including outbreaks involving multidrug-resistant strains of Mycobacterium tuberculosis, have heightened concern about nosocomial transmission. In addition, increases in tuberculosis cases in many areas are related to the high risk of tuberculosis among persons infected with the human immunodeficiency virus (HIV). Transmission of tuberculosis to persons with HIV infection is of particular concern because they are at high risk of developing active tuberculosis if infected. Health-care workers should be particularly alert to the need for preventing tuberculosis transmission in settings in which persons with HIV infection receive care, especially settings in which cough-inducing procedures (e.g., sputum induction and aerosolized pentamidine [AP] treatments) are being performed. Transmission is most likely to occur from patients with unrecognized pulmonary or laryngeal tuberculosis who are not on effective antituberculosis therapy and have not been placed in tuberculosis (acid-fast bacilli [AFB]) isolation. Health-care facilities in which persons at high risk for tuberculosis work or receive care should periodically review their tuberculosis policies and procedures, and determine the actions necessary to minimize the risk of tuberculosis transmission in their particular settings. The prevention of tuberculosis transmission in health-care settings requires that all of the following basic approaches be used: a) prevention of the generation of infectious airborne particles (droplet nuclei) by early identification and treatment of persons with tuberculous infection and active tuberculosis, b) prevention of the spread of infectious droplet nuclei into the general air circulation by applying source-control methods, c) reduction of the number of infectious droplet nuclei in air contaminated with them, and d) surveillance of health-care-facility personnel for tuberculosis and tuberculous infection. Experience has shown that when inadequate attention is given to any of these approaches, the probability of tuberculosis transmission is increased. Specific actions to reduce the risk of tuberculosis transmission should include a) screening patients for active tuberculosis and tuberculous infection, b) providing rapid diagnostic services, c) prescribing appropriate curative and preventive therapy, d) maintaining physical measures to reduce microbial contamination of the air, e) providing isolation rooms for persons with, or suspected of having, infectious tuberculosis, f) screening health-care-facility personnel for tuberculous infection and tuberculosis, and g) promptly investigating and controlling outbreaks. Although completely eliminating the risk of tuberculosis transmission in all health-care settings may be impossible, adhering to these guidelines should minimize the risk to persons in these settings.

Published studies of the relation between type of building ventilation system and work-related symptom prevalence in office workers have been contradictory. A reanalysis was performed of six studies meeting specific eligibility criteria, combining published data with unpublished information obtained from study authors. Five eligible studies were from the United Kingdom, and one was from Denmark. Standardized categories of building ventilation type were created to allow comparison of effects across studies. Within each study, prevalence odds ratios (PORs) were calculated for symptoms in each ventilation category relative to a baseline category of naturally ventilated buildings. Air-conditioned buildings were consistently associated with increased prevalence of work-related headache (POR = 1.3-3.1), lethargy (POR = 1.4-5.1), and upper respiratory/mucus membrane symptoms (POR = 1.3-4.8). Humidification was not a necessary factor for the higher symptom prevalence associated with air-conditioning. Mechanical ventilation without air-conditioning was not associated with higher symptom prevalence. The consistent associations found between type of building ventilation and reported symptom prevalence have potentially important public health and economic implications.

Increased rates of nosocomial infection caused by filamentous fungi in immunocompromised patients prompted microbiologic surveillance of the central air handling systems in our hospital. During a 4-year period, Penicillium species were isolated from 47 patients, including two with surgical wound infections caused by Penicillium. Counts of Penicillium in operating room air were much higher (195 colony-forming units [CFU]/m3) than in 95% filtered corridor air (14.6 CFU/m3; p less than 0.01). Ventilation ducts and terminal units lined with fiberglass in the operating room air handling system were heavily contaminated by Penicillium; the fiberglass was also contaminated with Aspergillus species. Corrective measures included filter replacement and decontamination of the ventilation system with aerosolized chlorine solution. Although operating room air remained free of filamentous fungi during the next 7 months, contamination eventually recurred and required repeated decontamination. We believe that certification guidelines are highly desirable for hospital ventilation systems, especially if the system serves immunocompromised patients.

In this issue, we evaluate seven general-purpose laser smoke evacuators (one with two different filters) from seven manufacturers. All evacuators are specifically designed and marketed for use in the OR during general surgery. Studies have demonstrated that laser smoke contains particles and gases that are hazardous to the respiratory tract, and current standards of practice include the use of a dedicated smoke evacuator during open surgical laser procedures. Not enough information is yet available to determine whether a smoke evacuator should be used during any surgical procedure in which airborne particles are generated. We based our ratings primarily on the units' ability to capture the airborne particles generated at the surgical site and remove them from the air that is recirculated to the environment. Because filtration efficiency does not adequately describe a unit's performance, users should not base purchasing decisions on filtration efficiency alone, but should emphasize the unit's performance as demonstrated by our evaluation. We rated both the C.L.A.S.S.B-1 with its HEPA filter and the Coherent Evaculase XSE-500 Unacceptable because they failed to adequately reduce smoke concentration with optimal nozzle placement. We rated the C.L.A.S.S.B-1 with its ULPA filter, Gyne-Tech Microvac, Lase System II, Pfizer S.A.F.E. System, Stackhouse Point One System, and Surgimedics Surgifresh Acceptable; preferences among these units will depend on how they are used. We caution clinicians to base purchasing decisions on a thorough understanding of the issues behind our conclusions, which can be gained only by reading this evaluation in its entirety.

Efficiency of industrial local exhaust ventilation is defined as the ratio of air contaminant quantity captured by the system per unit time to the total contaminant quantity produced by the process per unit time. To date, no direct method exists for this evaluation. This paper describes a tracer gas technique, using sulfur hexafluoride (SF6), which has been developed for the evaluation of local exhaust system efficiency. SF6 was discharged at a known rate into the industrial process generation area. Then, by comparing this quantity to that captured by the exhaust system, as measured in the exhaust duct, hood efficiency is determined. Major advantages of this technique are: The tracer gas technique is able to evaluate directly the hood efficiency. The tracer gas technique is not affected by cross-contamination from nearby industrial processes. The tracer gas technique can be conducted "on site" with minimal interruption of industrial process or interference with workers' duties. The tracer gas, using SF6 is non-toxic. Since SF6 is a gas, this technique may be limited to efficiency evaluation of hoods associated with gases, fumes, vapors, or fine particles.

Because of insufficient ventilation during winter, water condensation associated with a high concentration of ammonia (70-100 ppm) in the air, occurred on several breeding farms. The ammonia became bound to the condensation water and was converted into nitrites (6000-16000 mg/l) and nitrates (1630-1700 mg/l). Ingestion by the birds resulted in acute death, probably as a result of the high nitrite concentration. The brown colour of the blood pointed to the conversion of haemoglobin to methaemoglobin and this is one of the features of nitrite poisoning.

Four bone marrow transplant recipients consecutively occupying the same room on our Oncology-Hematology Special Care Unit (OHSCU) became colonized with Chaetomium species between January and April, 1987. These patients, aged 27 to 43 years, were immunocompromised as a result of intensive chemotherapy, and were consequently at increased risk for development of invasive fungal infection. At the time of Chaetomium colonization, all patients were febrile, two had transient new infiltrates on chest x-ray, and three were receiving amphotericin B therapy. Subsequent environmental cultures revealed Chaetomium contamination of the OHSCU air-handling system, including the HEPA (high-efficiency particulate air) filters in seven of the nine rooms comprising the unit. Because fungal colonization of HEPA filters used to create a "protective environment" for immunocompromised patients can occur and can serve as a source for patient infections, guidelines concerning proper surveillance of these HEPA filters should be established. We suggest that before a new patient enters a "protected" room, the clean side of the HEPA filter should be cultured. If fungi are recovered from that culture, we would recommend changing the filter.

The present report is a research on air samples taken in the operating theatres environment in the hospitals of Umbria to control in order the concentration of anaesthetics in use and to define ambient pollution and to propose changes. The A.A. have divided operating theatres in for groups to analyze the data: 1) operating theatres where there were both systems: air change system and air intake system; 2) operating theatres where there was only the air-change system; 3) operating theatres where there was only the air intake system; 4) operating theatres where there were no systems. These data have been compared with the limit values advised by N.I.O.S.H. The lowest value of pollution have been recorded in those operating theatres with both systems. The A.A. have also compared the ethrane or other alogenated anaesthetics values in the air-change system equipped operating theatres with those (values) found in the intake-air system equipped operating theatres. The lowest values have been recorded in those operating theatres with normal air-change system. Where changes have been made to improve the operating theatres environment, the A.A. have effectuated new controls and found lower values of the anaesthetics levels. The concentration of anaesthetics appeared lower then before.

Proper air change rates and venting systems in hospital central service sterilization rooms can reduce employees' exposure to ethylene oxide.

Design and performance information on a filtered-air positive-pressure (FAPP) housing system for disease-free poultry flocks is presented. The system includes many special features that result in excellent biological security, easy cleanup and maintenance, efficient control of environment, and a centralized alarm in the event of problems. The system has now housed eight flocks without any major problems. Based on its performance thus far, it should be useful as a reliable housing system for disease-free poultry.

The application of process control to mine ventilation, as described in this paper, has two aims 1. to improve safety in mines, by a rapid and, if possible, continuous matching of the air distribution with the variable methane and heat emissions in the mine workings, 2. to limit the adverse effects of perturbation in the mine ventilation system. The principles are discussed and the computer flow sheets given. The colliery where the installation is proposed, is presented. Pressure, air flow, methane concentration, temperature and humidity are measured underground. Readings are collected and transmitted through the telephone network to a computer where they are processed in real time. The next step will be to install the airflow regulating devices and to control them remotely by computer. The computer programs will be progressively introduced in the control routine. Nevertheless, the important regulating actions will not, at least during the initial period, be automaticaly executed unless supervised by man.

Environmental tobacco smoke is of serious concern in ventilated spaces both for comfort because of its odor properties and for health reasons. Although it has not been demonstrated as the primary cause in complaints, it is frequently seen as a contributing factor. Recirculation of air with ETS, without filtration or air-washing, may in fact lead to complaints, although at an unknown frequency. Finally, the contributions of ETS to the sick building syndrome is documented, although its extent is currently unknown.

Epidemiologic and animal studies indicate that chronic exposure to anesthetic gases may consitute a potential health hazard. This is suggested by a higher incidence of spontaneous abortion among female operating room personnel, congenital anomalies in the offspring of operating room personnel, and neoplasia of the reticuloendothelial system. Human data show that performance can be compromised during exposure to anesthetic traces. A direct cause and effect relationship between anesthetic exposure and the alleged hazards will require further prospective studies. Such a study is being planned by the Ad Hoc Committee of the American Society of Anesthesiologists. In the interim, monitoring programs should be established to define adequate clearances of the anesthetic agents. Minimum standards and recommended procedures should be established regarding operating room ventilation and design. The use of effective scavengers and anesthetic techniques not requiring the use of inhalational agents should be encouraged. In this way a clear distinction may be defined by the prosepective study planned by the American Society of Anesthesiologists in 1978.