Influence of room geometry and ventilation rate on airflow and aerosol dispersion: implications for worker protection.

Knowledge of dispersion rates and patterns of radioactive aerosols and gases through workrooms is critical for understanding human exposure and for developing strategies for worker protection. The dispersion within rooms can be influenced by complex interactions between numerous variables, but especially ventilation design and room furnishings. For this study, dependence of airflow and aerosol dispersion on workroom geometry (furnishings) and ventilation rate were studied in an experimental room that was designed to approximate a plutonium laboratory. Three different configurations of simulated gloveboxes and two ventilation rates (approximately 6 and 12 air exchanges per hour) were studied. A sonic anemometer was used to measure airflow parameters including all three components of air velocity vectors and turbulence intensity distributions at multiple locations and heights. Aerosol dispersion rates and patterns were measured by releasing aerosols multiple times from six different locations. Aerosol particle concentrations resolved in time and space were measured using 16 multiplexed laser particle counters. Comparisons were made of air velocities, turbulence, and aerosol transport across different ventilation rates and room configurations. A strong influence of ventilation rate on aerosol dispersion rates and air velocity was found, and changes in room geometry had significant effects on aerosol dispersion rates and patterns. These results are important with regards to constant evaluation of placement of air sampling equipment, benchmarking numerical models of room airflow, and design of ventilation and room layouts with consideration of worker safety.     

Identification of factors that disrupt negative air pressurization of respiratory isolation rooms.

OBJECTIVES: To investigate the airflow characteristics of respiratory isolation rooms (IRs) and to evaluate the use of visible smoke as a monitoring tool. METHODS: Industrial hygienists from the New York State Department of Health evaluated 140 designated IRs in 38 facilities within New York State during 1992 to 1998. The rooms were located in the following settings: hospitals (59%), correctional facilities (40%), and nursing homes (1%). Each room was tested with visible smoke for directional airflow into the patient room (ie, negative air pressure relative to adjacent areas). Information was obtained on each facility's policies and procedures for maintaining and monitoring the operation of the IRs. RESULTS: Inappropriate outward airflow was observed in 38% of the IRs tested. Multiple factors were associated with outward airflow direction, including ventilation systems not balanced (54% of failed rooms), shared anterooms (14%), turbulent airflow patterns (11%), and automated control system inaccuracies (10%). Of the 140 tested rooms, 38 (27%) had either electrical or mechanical devices to monitor air pressurization continuously. The direction of airflow at the door to 50% (19/38) of these rooms was the opposite of that indicated by the continuous monitors at the time of our evaluations. The inability of continuous monitors to indicate the direction of airflow was associated with instrument limitations (74%) and malfunction of the devices (26%). In one facility, daily smoke testing by infection control staff was responsible for identifying the malfunction of a state-of-the-art computerized ventilation monitoring and control system in a room housing a patient infectious with drug-resistant tuberculosis. CONCLUSION: A substantial percentage of IRs did not meet the negative air pressure criterion. These failures were associated with a variety of characteristics in the design and operation of the IRs. Our findings indicate that a balanced ventilation system does not guarantee inward airflow direction. Devices that continuously monitor and, in some cases, control the pressurization of IRs had poor reliability. This study demonstrates the utility of using visible smoke for testing directional airflow of IRs, whether or not continuous monitors are used. Institutional tuberculosis control pro grams should include provisions for appropriate monitoring and maintenance of IR systems on a frequent basis, including the use of visible smoke.     

An evaluation of hospital special-ventilation-room pressures.

OBJECTIVE: To quantitate the magnitude and consistency of positive (airflow out) and negative (airflow in) hospital special-ventilation-room (SVR) airflow. DESIGN: A room-pressure evaluation was conducted during two seasons on a total of 18 rooms: standard rooms, airborne infection isolation rooms, and protective environment rooms. The pressures were measured using a digital pressure gauge-piezoresistive pressure sensor that measured pressure differentials. With doors closed, the rooms were measured a minimum of 30 times each for a cooling season and a heating season. RESULTS: The standard rooms showed the least amount of variability in pressure differential, with an average of -0.2 Pa (median, -0.2 Pa), and an interquartile range (IQR) of 0.4 Pa. Airborne infection isolation rooms showed more variability in pressure, with an average of -0.3 Pa (median, -0.2 Pa) and an IQR of 0.5 Pa. Protective environment rooms had the greatest fluctuation in pressure, with an average of 8.3 Pa (median, 7.7 Pa) and an IQR of 8.8 Pa. Dramatic pressure changes were observed during this evaluation, which may have been influenced by room architectural differences (sealed vs unsealed); heating, ventilation, and air-conditioning zone interactions; and stack effect. CONCLUSION: The pressure variations noted in this study, which potentially affect containment or exclusion of contaminants, support the need for standardization of pressure requirements for SVRs. To maintain consistent pressure levels, creating an airtight seal and continuous pressure monitoring may be necessary.     

Method for installing an effective smoking room and the effectiveness of real-time monitoring]

We investigated the methodology for installing effective smoking rooms in workplaces. It is absolutely necessary to install exhaust ventilation in smoking rooms. There are two bases for deciding the exhaust ventilation rate. The most important is to eliminate the leakage of environmental tobacco smoke (ETS) from the smoking room. An airflow rate of more than 0.2 m/s at the opening of the smoking room is required by the Guidelines for Smoking Control in Workplaces (Ministry of Labour, Welfare and Health) to eliminate the leakage. This ventilation rate is decided by multiplying the opening area by 0.2 m/s. The second important point is to keep the concentration of ETS in the smoking room less than control concentration (0.15 mg/m3). This ventilation rate is decided by dividing the rate of generation of ETS by the control concentration. It is confirmed that an effective smoking room can be installed by following these guidelines. We used real-time monitoring to evaluate the leakage of ETS from the smoking room and the ETS concentration in the smoking room before and after the improvement. It is concluded that real-time monitoring of ETS is a useful method for evaluating the effectiveness of the smoking room.     

乱流洁净室中换气次数对污染物扩散影响的数值模拟

针对孔板送风的乱流洁净室，运用CFD软件对不同换气次数条件下的气流组织和污染物扩散进行数值模拟分析。通过对15～70换气次数的洁净室的数值模拟，比较了不同换气次数下洁净室的排污效率；通过模拟对比，得出在换气次数为55次时．房间的排污效率最好；并为工程设计提供了一定的理论依据。     

A simple method for tracer containment testing of hospital isolation rooms

A simple method for tracer containment testing of hospital isolation rooms is presented. The method does not require any equipment setup in tested rooms and can be completed in approximately one-half hour per room. Tracer samples are taken at specified time intervals in the corridor outside of an isolation room and analyzed on a portable gas chromatograph system. Results are presented from tracer testing of two isolation rooms in two different hospitals. One isolation room had a significant negative pressure differential between room and corridor, and the other isolation room was not at negative pressure. A small quantity of sulfur hexafluoride gas was injected manually from a polyethylene syringe over a bed in an isolation room. Tracer concentrations were thereafter measured in the corridor adjacent to the room at 5-minute intervals for 20 minutes after the injection, yielding a quantitative measure of leakage of the tracer from the isolation room. Finally, measuring the tracer concentration in the isolation room 30 minutes after injection yielded an indication of how effectively the ventilation system removed a contaminant released at the position of the bed. The results show that an instantaneous release of a small quantity of tracer gas in an isolation room yields tracer concentrations in the corridor outside of the room that are within the analytical range of the measuring equipment both for a properly functioning isolation room and an improperly functioning isolation room, and thus that the method is well-suited for studying containment in hospital isolation rooms. Possible practical applications of the method are discussed.     

A ten-year risk evaluation study in Catania hospital operating rooms

Previous studies conducted in Catania hospitals have revealed a high burden of contamination in the air of operating rooms and have recommended measures to improve air quality. In this study we verified the effectiveness of the undertaken measures. Furthermore we evaluated the possibility of using microclimatic parameters as "markers" of operating room contamination. Changes made to ventilation systems and to waste gas scavenging systems in the monitored operating rooms were remarkably effective. Microclimatic conditions and degree of chemical contamination improved over time; nevertheless airflow velocity values were found to be insufficient and nitrous oxide values, in some cases, remained slightly elevated. A significant correlation was observed only between some nitrous oxide values and relative humidity. Monitoring important marker levels is useful for correctly evaluating operating room thermal, chemical and microbiological air quality.     

Tuberculosis isolation: comparison of written procedures and actual practices in three California hospitals.

OBJECTIVE: To evaluate implementation of healthcare worker exposure control measures for tuberculosis (TB)-patient isolation, as specified by Centers for Disease Control and Prevention (CDC) guidelines and the hospital's TB-control policy. DESIGN: Prospective multihospital study comparing CDC guidelines and hospital policy for TB-patient isolation to once-weekly observations of TB-patient isolation practices over 14 consecutive weeks at each hospital. SETTING: Three urban hospitals (two county, one private community) in counties in California with a high incidence rate of TB. MEASUREMENTS: Work practices for TB-patient isolation were observed and ventilation performance of isolation rooms was assessed while patient rooms were in use for TB isolation. RESULTS: Of 170 TB-patient rooms observed, 119 (70%) involved a patient in a designated TB isolation room, the room was under negative pressure, the door was closed, and a "respiratory precautions" sign was on the door; 32 patient-room units (19%) were not under negative pressure or not designated as negative-pressure rooms. Of 151 patient-room units mechanically capable of negative pressure at a prior point in time, 16 (11%) were not under negative pressure at the time of use. Of 67 patient-room units equipped with continuous monitoring devices, 8 (12%) involved devices that did not accurately reflect the direction of airflow. Of the 62 healthcare workers observed using a respirator for TB, 40 (65%) did not don the respirator properly. CONCLUSIONS: Implementing CDC guidelines for TB-patient isolation was feasible but imperfect in the three hospitals. Day-to-day work practices deviated from hospital policy. Prospectively quantifying the implementation of a hospital TB isolation policy while the room is in use may lead to improved estimates of risk and may help to identify and thereby prevent avoidable healthcare worker exposures to Mycobacterium tuberculosis aerosol. Auditing practices and verifying equipment performance is likely to identify unexpected problems in implementation of the TB control program.     

Residential inter-zonal ventilation rates for exposure modeling

Residential inter-zonal (e.g., between rooms) ventilation is comprised of fresh air infiltration in and exfiltration out of the whole house plus the “fresh” air that is entering (and exiting) the room of interest from other rooms or areas within the house. Clearly, the inter-zone ventilation rate in any room of interest will be greater than the infiltration/exfiltration ventilation rate of outdoor air for the whole house. The purpose of this study is to determine how much greater the inter-zonal ventilation rate is in typical U.S. residences compared to the whole house ventilation rate from outdoor air. The data for this statistical analysis came from HouseDB, a 1995 EPA database of residential ventilation rates. Analytical results indicate that a lognormal distribution provides the best fit to the data. Lognormal probability distribution functions (PDFs) are provided for various inter-zonal ventilation rates for comparison to the PDF for the whole house ventilation rates. All ventilation rates are expressed as air change rates per hour (ACH). These PDFs can be used as inputs to exposure models. This analysis suggests that if one were performing a deterministic analysis for unknown housing stocks in the U.S., a default mean and median ACH values of 0.4/hr and 0.3/hr, respectively, for whole house ventilation would be appropriate; and 0.7/hr and 0.6/hr, respectively, for inter-zonal ventilation.     

The effectiveness of radon remediation in Irish schools

An advisory reference level of 200 Bq m(-3) and a statutory reference level of 400 Bq m(-3) apply to radon exposure in Irish schools. Following the results of a national survey of radon in Irish schools, several hundred classrooms were identified in which the reference levels were exceeded and a remediation program was put in place. This paper provides an initial analysis of the effectiveness of that remediation program. All remediation techniques proved successful in reducing radon concentrations. Active systems such as radon sumps and fan assisted under-floor ventilation were generally applied in rooms with radon concentrations above 400 Bq m(-3). These proved most effective with average radon reduction factors of 9 to 34 being achieved for radon sumps and 13 to 57 for fan assisted under-floor ventilation. Both of these techniques achieved maximum radon reduction factors in excess of 100. The highest average reduction factors were associated with the highest initial radon concentrations. Passive remediation systems such as wall and window vents were used to increase background ventilation in rooms with radon concentrations below 400 Bq m(-3) and achieved average radon reductions of approximately 55%. Following the installation of active remediation systems, the radon concentration in adjacent rooms, i.e., rooms in which the radon concentration was already below 200 Bq m(-3) and therefore did not require remediation, was further reduced by an average of 25%. The long-term effectiveness of a number of radon sump systems with at least three years operation showed no evidence of fan failures. This study showed an apparent increase in sump effectiveness with time as indicated by an increase in radon reduction factors during this period.     

Hospital and community acquired infection and the built environment--design and testing of infection control rooms

Negative-pressure isolation rooms are required to house patients infected with agents transmissible by the aerosol route in order to minimise exposure of healthcare workers and other patients. Housing patients in a separate room provides a barrier which minimises any physical contact with other patients. An isolation room held at negative pressure to reduce aerosol escape and a high air-change rate to allow rapid removal of aerosols can eliminate transmission of infectious aerosols to those outside the room. However, badly designed and/or incorrectly operating isolation rooms have been shown to place healthcare workers and other patients at risk from airborne diseases such as tuberculosis. Few standards are available for the design of isolation rooms and no pressure differential or air-change rates are specified. Techniques such as aerosol particle tracer sampling and computational fluid dynamics can be applied to study the performance of negative-pressure rooms and to assess how design variables can affect their performance. This should allow cost-effective designs for isolation rooms to be developed. Healthcare staff should be trained to understand how these rooms operate and there should be systems in place to ensure they are functioning correctly.     

Containment testing of isolation rooms

Results from the tracer containment testing of four 'state-of-the-art' airborne infection isolation rooms, in a new hospital, are presented. A testing technician exited an isolation room several minutes after a small quantity of tracer gas was injected over the patient bed in that room. Easily measurable tracer gas concentrations were then found in the anterooms outside the patient rooms and corridor outside the isolation room suites. Containment factors for the isolation rooms and dilution factors in the anterooms and corridor were calculated, based on the measured tracer concentrations. These results indicate the desirability of evidence-based design standards and guidelines for assessing performance of airborne infection isolation rooms. The study also demonstrates that the tracer testing procedure yields comparable results for equivalent isolation room suites, suggesting good reproducibility of the testing method.     

Environmental and occupational health response to SARS, Taiwan, 2003

Industrial hygiene specialists from the National Institute for Occupational Safety and Health (NIOSH) visited hospitals and medical centers throughout Taiwan. They assisted with designing and evaluating ventilation modifications for infection control, developed guidelines for converting hospital rooms into SARS patient isolation rooms, prepared designs for the rapid conversion of a vacated military facility into a SARS screening and observation facility, assessed environmental aspects of dedicated SARS hospitals, and worked in concert with the Taiwanese to develop hospital ventilation guidelines. We describe the environmental findings and observations from this response, including the rapid reconfiguration of medical facilities during a national health emergency, and discuss environmental challenges should SARS or a SARS-like virus emerge again.     

Considerations on isolation rooms and alternative pressure ventilation systems

The health-care facility environment is involved in disease transmission in essentially two different situations: 1. in cases where patients are immunocompromised and require protection from infections; 2. in cases of inadvertent exposure to environmental or airborne pathogens that can aggravate patients' existent disease and cause illness among health-care personnel. Environmental infection-control strategies and engineering controls can effectively prevent transmission of these infections. In particular the ventilation system is fundamental to the control of the concentration of airborne contaminants within a hospital isolation room because it establishes and maintains appropriate pressure differentials within special care areas of the building. Thus the incidence of health-care-associated infections can be minimized by adherence to ventilation standards suggested in the guidelines for specialized care environments such as Airborne Infection Isolation rooms (AII, as in situation 2 above), and Protective Environments (PE) rooms (as in situation 1 above). This report is a comparative review of the principal guidelines and strategies existing in the international scientific literature for the prevention of environment-associated infections in healthcare facilities using pressure differentials (positive pressure for PE rooms, negative pressure for AII rooms). The purpose of the review is also to investigate the state-of-the-art use of the "alternative pressure rooms", i.e., areas furnished with a ventilation system capable of switching pressure from positive to negative according to patients' needs. The results of the present analysis indicate an unenthusiastic reaction to these "alternative pressure rooms", although there is no scientific evidence against their use.     

Evaluation of source model coupled computational fluid dynamics (CFD) simulation of the dispersion of airborne contaminants in a work environment

Dispersion of airborne contaminants in indoor air was evaluated employing physical measurement, empirical models, and computer simulation methods. Field data collected from a tray of evaporating solvent in the laboratory were compared with computational fluid dynamics (CFD) simulations coupled with evaporation models. The results indicated that mathematical models of evaporation can be coupled with CFD simulations to produce reasonable qualitative predictions of airborne contaminant levels. The airflow pattern within a room is primarily determined by the room layout and the position of the air supply diffusers. Variations in ventilation rate did not alter the airflow pattern, thus generating a characteristic concentration profile of the airborne contaminants.     

SARS流行期间空调及通风系统的管理

目的 探讨SARS流行期间空调系统的安全使用方法及如何利用现有的通风系统形成隔离病房内负压，有效控制SARS感染的传播。方法 对北京市6所SARS定点收治医院和3所三级甲等综合医院的空调及排风系统进行实地调研。结果 调查的9所医院空调系统均可以使用；利用现有通风条件可以达到空气流通的效果；应用排风系统可以形成隔离病房内负压，但不能有效控制空气流向。结论 风机盘管加新风空调系统和分体式房间空调系统可以安全使用，隔离病房内通风系统在满足一定条件时可以形成有效负压。     

医院中央空调通风系统消毒管理现状调查与循证干预

目的探讨循证干预在中央空调通风系统消毒管理中的应用。方法在对医院中央空调运行管理现状调查的基础上,充分利用先进的科学技术及经验,对中央空调通风系统管理实施循证干预。结果医院中央空调系统管理存在诸多薄弱环节,新风机房符合规范要求的占42.9%;出风口存在真菌菌斑的占61.3%;对于中央空调管理存在认识盲区的员工占69.1%;由此针对中央空调系统的设施管理、人员培训和卫生管理,实施循证干预并加以改进。结论建立在有充分科学证据的基础之上循证干预措施,是提高中央空调通风系统消毒管理质量,保障医疗安全的有效手段之一。     

Probable Aerosol Transmission of SARS-CoV-2 through Floors and Walls of Quarantine Hotel,Taiwan, 2021

We investigated a cluster of SARS-CoV-2 infections in a quarantine hotel in Taiwan in December 2021. The cluster involved 3 case patients who lived in nonadjacent rooms on different floors. They had no direct contact during their stay. By direct exploration of the space above the room ceilings, we found residual tunnels, wall defects, and truncated pipes between their rooms. We conducted a simplified tracer-gas experiment to assess the interconnection between rooms. Aerosol transmission through structural defects in floors and walls in this poorly ventilated hotel was the most likely route of virus transmission. This event demonstrates the high transmissibility of Omicron variants, even across rooms and floors, through structural defects. Our findings emphasize the importance of ventilation and integrity of building structure in quarantine facilities.     

Airborne infection in a fully air-conditioned hospital. II. Transport of gaseous and airborne particulate material along ventilated passageways.

A mathematical model is described for the transport of gaseous or airborne particulate material between rooms along ventilated passageways. Experimental observations in three hospitals lead to a value of about 0.06 m.2/sec. for the effective diffusion constant in air without any systematic directional flow. The ''constant'' appears to increase if there is any directional flow along the passage, reaching about 0.12 m. 2/sec. at a flow velocity of 0.04 m./sec. Together with previously published methods the present formulae make it possible to calculate the expected average amounts of gaseous or particulate material that will be transported from room to room in ventilated buildings in which the ventilation and exchange airflows can be calculated. The actual amounts transported in occupied buildings, however, vary greatly from time to time.     

BSL-3实验室内不同负压对定向气流影响的数值研究

目的：讨论BSL-3主实验室内不同负压状态对定向气流影响以及门缝渗风对气流的影响。方法：利用数值模拟与实验测试相结合方法进行研究。结果：在保证BSL-3实验室主实验室送风量不变的情况下,负压大小是影响实验室气流组织的关键因素。结论：在-50 Pa的状态下能形成较好的定向气流形式。