Preventing carbon monoxide poisoning in the Hudson River Tunnel in 1921: recounting history

The New York Bridge and Tunnel Commission began planning for a tunnel beneath the lower Hudson river to connect Manhattan to New Jersey in 1919. At 8,300 feet, it would be the longest tunnel for passenger vehicles in the world. A team of engineers and physiologists at the Yale University Bureau of Mines Experiment Station was tasked with calculating the ventilation requirements that would provide safety from exposure to automobile exhaust carbon monoxide (CO) while balancing the cost of providing ventilation. As the level of ambient CO which was comfortably tolerated was not precisely defined, they performed human exposures breathing from 100 to 1,000 ppm CO, first on themselves and subsequently on Yale medical students. Their findings continue to provide a basis for carbon monoxide alarm requirements a century later.

Cost-benefit analysis of different air change rates in an operating room environment

BACKGROUND

Hospitals face growing pressure to meet the dual but often competing goals of providing a safe environment while controlling operating costs. Evidence-based data are needed to provide insight for facility management practices to support these goals.

METHODS

The quality of the air in 3 operating rooms was measured at different ventilation rates. The energy cost to provide the heating, ventilation, and air conditioning to the rooms was estimated to provide a cost-benefit comparison of the effectiveness of different ventilation rates currently used in the health care industry.

RESULTS

Simply increasing air change rates in the operating rooms tested did not necessarily provide an overall cleaner environment, but did substantially increase energy consumption and costs. Additionally, and unexpectedly, significant differences in microbial load and air velocity were detected between the sterile fields and back instrument tables.

CONCLUSIONS

Increasing the ventilation rates in operating rooms in an effort to improve clinical outcomes and potentially reduce surgical site infections does not necessarily provide cleaner air, but does typically increase operating costs. Efficient distribution or management of the air can improve quality indicators and potentially reduce the number of air changes required. Measurable environmental quality indicators could be used in lieu of or in addition to air change rate requirements to optimize cost and quality for an operating room and other critical environments.

The ventilation problem in schools: literature review

Based on a review of literature published in refereed archival journals, ventilation rates in classrooms often fall far short of the minimum ventilation rates specified in standards. There is compelling evidence, from both cross-sectional and intervention studies, of an association of increased student performance with increased ventilation rates. There is evidence that reduced respiratory health effects and reduced student absence are associated with increased ventilation rates. Increasing ventilation rates in schools imposes energy costs and can increase heating, ventilating, and air-conditioning system capital costs. The net annual costs, ranging from a few dollars to about 10 dollars per person, are less than 0.1% of typical public spending on elementary and secondary education in the United States. Such expenditures seem like a small price to pay given the evidence of health and performance benefits.

Effectiveness and cost of reducing particle-related mortality with particle filtration

This study evaluates the mortality-related benefits and costs of improvements in particle filtration in U.S. homes and commercial buildings based on models with empirical inputs. The models account for time spent in various environments as well as activity levels and associated breathing rates. The scenarios evaluated include improvements in filter efficiencies in both forced-air heating and cooling systems of homes and heating, ventilating, and air conditioning systems of workplaces as well as use of portable air cleaners in homes. The predicted reductions in mortality range from approximately 0.25 to 2.4 per 10 000 population. The largest reductions in mortality were from interventions with continuously operating portable air cleaners in homes because, given our scenarios, these portable air cleaners with HEPA filters most reduced particle exposures. For some interventions, predicted annual mortality-related economic benefits exceed $1000 per person. Economic benefits always exceed costs with benefit-to-cost ratios ranging from approximately 3.9 to 133. Restricting interventions to homes of the elderly further increases the mortality reductions per unit population and the benefit-to-cost ratios.

Perceptions in the U.S. building industry of the benefits and costs of improving indoor air quality

How building stakeholders (e.g. owners, tenants, operators, and designers) understand impacts of Indoor Air Quality (IAQ) and associated energy costs is unknown. We surveyed 112 stakeholders across the United States to ascertain their perceptions of their current IAQ and estimates of benefits and costs of, as well as willingness to pay for, IAQ improvements. Respondents' perceived IAQ scores correlated with the use of high-efficiency filters but not with any other IAQ-improving technologies. We elicited their estimates of the impacts of a ventilation-filtration upgrade (VFU), that is, doubling the ventilation rate from 20 to 40 cfm/person (9.5 to 19 l/s/person) and upgrading from a minimum efficiency reporting value 6 to 11 filter, and compared responses to estimates derived from IAQ literature and energy modeling. Minorities of respondents thought the VFU would positively impact productivity (45%), absenteeism (23%), or health (39%). Respondents' annual VFU cost estimates (mean = $257, s.d. = $496, median = $75 per person) were much higher than ours (always <$32 per person), and the only yearly cost a plurality of respondents said they would pay for the VFU was $15 per person. Respondents holding green building credentials were not more likely to affirm the IAQ benefits of the VFU and were less likely to be willing to pay for it.

Economic, Environmental and Health Implications of Enhanced Ventilation in Office Buildings

Introduction: Current building ventilation standards are based on acceptable minimums. Three decades of research demonstrates the human health benefits of increased ventilation above these minimums. Recent research also shows the benefits on human decision-making performance in office workers, which translates to increased productivity. However, adoption of enhanced ventilation strategies is lagging. We sought to evaluate two of the perceived potential barriers to more widespread adoption—Economic and environmental costs. Methods: We estimated the energy consumption and associated per building occupant costs for office buildings in seven U.S. cities, representing different climate zones for three ventilation scenarios (standard practice (20 cfm/person), 30% enhanced ventilation, and 40 cfm/person) and four different heating, ventilation and air conditioning (HVAC) system strategies (Variable Air Volume (VAV) with reheat and a Fan Coil Unit (FCU), both with and without an energy recovery ventilator). We also estimated emissions of greenhouse gases associated with this increased energy usage, and, for comparison, converted this to the equivalent number of vehicles using greenhouse gas equivalencies. Lastly, we paired results from our previous research on cognitive function and ventilation with labor statistics to estimate the economic benefit of increased productivity associated with increasing ventilation rates. Results: Doubling the ventilation rate from the American Society of Heating, Refrigeration and Air-Conditioning Engineers minimum cost less than $40 per person per year in all climate zones investigated. Using an energy recovery ventilation system significantly reduced energy costs, and in some scenarios led to a net savings. At the highest ventilation rate, adding an ERV essentially neutralized the environmental impact of enhanced ventilation (0.03 additional cars on the road per building across all cities). The same change in ventilation improved the performance of workers by 8%, equivalent to a $6500 increase in employee productivity each year. Reduced absenteeism and improved health are also seen with enhanced ventilation. Conclusions: The health benefits associated with enhanced ventilation rates far exceed the per-person energy costs relative to salary costs. Environmental impacts can be mitigated at regional, building, and individual-level scales through the transition to renewable energy sources, adoption of energy efficient systems and ventilation strategies, and promotion of other sustainable policies.

Energy and cost associated with ventilating office buildings in a tropical climate

Providing sufficient amounts of outdoor air to occupants is a critical building function for supporting occupant health, well-being and productivity. In tropical climates, high ventilation rates require substantial amounts of energy to cool and dehumidify supply air. This study evaluates the energy consumption and associated cost for thermally conditioning outdoor air provided for building ventilation in tropical climates, considering Singapore as an example locale. We investigated the influence on energy consumption and cost of the following factors: outdoor air temperature and humidity, ventilation rate (L/s per person), indoor air temperature and humidity, air conditioning system coefficient of performance (COP), and cost of electricity. Results show that dehumidification of outdoor air accounts for more than 80% of the energy needed for building ventilation in Singapore's tropical climate. Improved system performance and/or a small increase in the indoor temperature set point would permit relatively large ventilation rates (such as 25 L/s per person) at modest or no cost increment. Overall, even in a thermally demanding tropical climate, the energy cost associated with increasing ventilation rate up to 25 L/s per person is less than 1% of the wages of an office worker in an advanced economy like Singapore's. This result implies that the benefits of increasing outdoor air ventilation rate up to 25 L/s per person--which is suggested to provide for productivity increases, lower sick building syndrome symptom prevalence, and reduced sick leave--can be much larger than the incremental cost of ventilation.

Evaluation of thermal comfort conditions in a classroom with three ventilation methods

Thermal sensation is studied experimentally under mixing ventilation, displacement ventilation, and stratum ventilation in an environmental chamber. Forty-eight subjects participated in all tests under the same boundary conditions but different ventilation methods in the classroom. Thermal comfort analysis was carried out according to the designated supply airflow rate, room temperature, and relative humidity for the three ventilation methods. The thermal neutral temperature under stratum ventilation is approximately 2.5 °C higher than that under mixing ventilation and 2.0 °C higher than that under displacement ventilation. This result indicates that stratum ventilation could provide satisfactory thermal comfort level to rooms of temperature up to 27 °C. The energy saving attributable to less ventilation load alone is around 12% compared with mixing ventilation and 9% compared with displacement ventilation.

PRACTICAL IMPLICATIONS

The confirmation of the significantly elevated thermal neutral temperature can have a number of implications for both thermal comfort in an air-conditioned room and energy consumption of the associate air-conditioning system. With respect to the former, it provides scientific basis for the feasibility of elevated room temperatures, and with respect to the latter, it reveals considerable potentials for energy saving.

Long duration tests of room air filters in cigarette smokers' homes

Information regarding the long-term performance of stand-alone room airfilters is limited. In this study, laboratory and field tests were carried out to determine the effectiveness and performance of room filters that are easily deployed in essentially any type of house. Tests were conducted in houses containing strong PM sources, specifically cigarette smokers. Using commercially available four-speed HEPA filter units, we tested flow rate, pressure drop, and power consumption as a function of fan speed and filter loading. Filters were then deployed in four single-family homes over a 2 month period. Between 15 and 40 cigarettes were smoked daily by several smokers in each home. Occupants were instructed to continuously operate the unit at one of the higher speeds. Periodically, we monitored filter usage, fan speed, particulate matter (PM) mass concentrations, PM number concentrations, volatile organic compound (VOC) levels, and other parameters with the filter fan operating and with filters both installed and removed. The filters decreased PM concentrations by 30-70%, depending on size fraction and occupant activities, and significantly reduced the half-life of PM3-1.0. The half-life of 1-5 microm particles, CO2 concentrations, and VOC concentrations, including 2,5-dimethyl furan (a tracer for environmental tobacco smoke), did not change, indicating that occupancy and cigarette smoking intensity did not change overthe monitoring periods. Occupants generally kept the filters operating at a moderate speed. Filter air flow rates decreased 7-14% with extended operation, largely due to the loading of prefilters. Air exchange rates, deposition loss rates, and clean air delivery rates were estimated from the field data. Continuous operation at an intermediate fan speed would incur a total annualized cost of $236. While acceptance of the filters was very high, occupants might benefit from instructions and reminders to clean the prefilter and to keep the unit on. We conclude that adequately sized room air filters can substantially lower PM concentrations in smoker's homes if air exchange rates are limited and that the filters can maintain their performance over extended periods.

An evaluation of portable high-efficiency particulate air filtration for expedient patient isolation in epidemic and emergency response

Extraordinary incidents resulting in airborne infectious disease outbreaks could produce patient isolation requirements that exceed most hospitals' capacity. This article investigates expedient methods to establish airborne infection isolation areas using a commercially available portable filtration unit and common hardware supplies. The study was conducted within a conventional, nonisolation hospital room, and researchers evaluated several airborne isolation configurations that did not require building ventilation or structural modifications. A portable high-efficiency particulate air filtration unit and full-length plastic curtains established a “zone-within-zone” protective environment using local capture and directional airflows. The cost of constructing the expedient configurations was less than US$2,300 and required fewer than 3 person-hours to construct. A medical nebulizer aerosolized polystyrene latex microspheres to generate respirable condensation nuclei. Aerosol spectrometers sized and counted respirable particles at the source patient and health care worker positions and in areas outside the inner zone. The best-performing designs showed no measurable source migration out of the inner isolation zone and mean respirable particle counts up to 87% lower at the health care worker position(s) than those observed directly near the source patient location. Investigators conclude that with careful implementation under emergency circumstances in which engineered isolation rooms are unavailable, expedient methods can provide affordable and effective patient isolation while reducing exposure risks and potential disease transmission to health care workers, other patients, and visitors.

[Cost evaluation of a ventilation system for operating theatre: an ultraclean design versus a conventional one]

The postoperative infection has been recognized as a critical problem in healthcare, increasing patients'complications and hospitalization costs. At the moment the scientific evidence clearly linking ventilation parameters, such as air changes per hour, bacterial counts and infection, is lacking, with the exception of prosthetic joint surgery. This study aims to evaluate the building and operating costs of an ultraclean system versus a conventional one (which satisfies the minimum performance requested by rules), also considering the debating efficacy of ultraclean ventilation on prevention of postoperative infection. The results of our study show an increase of 24% in the building costs and of 34% in the annual operating costs for the ultraclean system versus the conventional one. The estimated 24% increase of the building costs for the ultraclean ventilation system represents only a 5% increase if compared to the total cost of a not equipped operating theatre. Therefore, the increase on costs linked to the use of high performance ventilation facilities seems to be so small that overcoming current rules towards ultraclean systems could be acceptable.

Validation for a recirculation model

Recent Clean Air Act regulations designed to reduce volatile organic compound (VOC) emissions have placed new restrictions on painting operations. Treating large volumes of air which contain dilute quantities of VOCs can be expensive. Recirculating some fraction of the air allows an operator to comply with environmental regulations at reduced cost. However, there is a potential impact on employee safety because indoor pollutants will inevitably increase when air is recirculated. A computer model was developed, written in Microsoft Excel 97, to predict compliance costs and indoor air concentration changes with respect to changes in the level of recirculation for a given facility. The model predicts indoor air concentrations based on product usage and mass balance equations. This article validates the recirculation model using data collected from a C-130 aircraft painting facility at Hill Air Force Base, Utah. Air sampling data and air control cost quotes from vendors were collected for the Hill AFB painting facility and compared to the model's predictions. The model's predictions for strontium chromate and isocyanate air concentrations were generally between the maximum and minimum air sampling points with a tendency to predict near the maximum sampling points. The model's capital cost predictions for a thermal VOC control device ranged from a 14 percent underestimate to a 50 percent overestimate of the average cost quotes. A sensitivity analysis of the variables is also included. The model is demonstrated to be a good evaluation tool in understanding the impact of recirculation.

The impact of recirculating industrial air on aircraft painting operations

The 1990 Clean Air Act Amendments resulted in new environmental regulations for hazardous air pollutants. Industries such as painting facilities may have to treat large volumes of air, which increases the cost of an air control system. Recirculating a portion of the air back into the facility is an option to reduce the amount of air to be treated. The authors of this study developed a computer model written in Microsoft Excel 97 to analyze the impact of recirculation on worker safety and compliance costs. The model has a chemical database with over 1300 chemicals. The model will predict indoor air concentrations using mass balance calculations and results are compared to occupational exposure limits. A case study is performed on a C-130 aircraft painting facility at Hill Air Force Base, Utah. The model predicts strontium chromate concentrations found in primer paints will reach 1000 times the exposure limit. Strontium chromate and other solid particulates are nearly unaffected by recirculation because the air is filtered during recirculation. The next highest chemical, hexamethylene diisocyanate, increases from 2.6 to 10.5 times the exposure limit at 0 percent and 75 percent recirculation, respectively. Due to the level of respiratory protection required for the strontium chromate, workers are well protected from the modest increases in concentrations caused by recirculating 75 percent of the air. The initial cost of an air control system is $4.5 million with no recirculation and $1.8 million at 75 percent recirculation. The model is an excellent tool to evaluate air control options with a focus on worker safety. In the case study, the model highlights strontium chromate primers as good candidates for substitution. The model shows that recirculating 75 percent of the air at the Hill painting facility has a negligible impact on safety and could save $2.7 million on the initial expenses of a thermal treatment system.

Surgical smoke evacuation systems

Surgical smoke evacuation systems are high-flow vacuum sources used to capture, at the surgical site, the smoke aerosols and gases generated during the use of lasers and electrosurgical units (ESUs). In this study, we evaluated 16 evacuation systems, from 10 suppliers, designed and marketed for use in the operating room for general surgery. For our testing, we focused on the performance of the systems (particularly their ability to capture smoke particles under simulated surgical conditions) and their ease of use and quality of construction. We also examined the projected costs of each system over a seven-year life cycle. We rated the systems separately for two different evacuation applications (1) general-purpose applications, for which the system would, in many cases, be used with a handheld nozzle (the traditional capture device used with these systems), and (2) ESU-pencil-based evacuation applications only, for which the system would always be used with a pencil-based wand. (We report on ESU-pencil-based smoke evacuation wands in a separate Evaluation in this issue.) While we found most units to be Acceptable, we did rate two units Acceptable-Not Recommended for both applications and one unit Unacceptable for general-purpose applications. In addition to our findings for the evaluated models, this study features several sections providing generic information and guidance about smoke evacuation technology. The Technology Overview describes the basics: what these systems do and how they do it. The Technology Management Guide, "Clearing the Air-Should Surgical Smoke Be Evacuated?," discusses the issues healthcare facilities should consider when determining whether, when, and how surgical smoke should be evacuated. Finally, the Selection, Purchasing, and Use Guide offers guidance on how facilities can most effectively implement this technology, from identifying models that will meet their needs to ensuring that the systems are used properly to provide adequate staff protection.

Comfort and health: cause for concern

Chancellor Lamont's announcement in his 1993 Budget of the proposed imposition of VAT on domestic fuel bills, quoted in Hansard (1993), poses the question as to what effect this projected increase in fuel costs will have upon the health of those at greatest risk in the community. This paper is based upon the premise that householders on low, or fixed incomes faced with a significant increase in fuel costs must either reduce their expenditure or reduce their heating costs. The paper considers these issues and considers the possible effects upon standards of heating and ventilation in the home confounded by increased levels of insulation, and the potential for significant increases in condensation associated with increased levels of indoor air pollution within dwellings. Suggestions for the mitigation of these perceived risks to health are also set out, including the need for increased financial assistance for those most at risk.

An inexpensive system to monitor air flow in isolation units

Isolation units are used extensively for conducting infectious disease research in poultry. By necessity, these units are airtight and receive air only through electrically powered ventilation systems. Therefore, interruptions in electrical service to these units present a serious hazard to the animals they contain. A system was designed to monitor the air flow through isolation units and to alert animal caretakers in the event of any interruption in air flow. The "intelligence" of the system relies on an electronic monitor connected to a telephone line that places alerting telephone calls when it detects loss of air flow to the units. The system is constructed from easily acquired and relatively inexpensive parts and components.

Epidemiologic observations of operating room infections resulting from variations in ventilation and temperature

Over a period of years the ventilation system of a community hospital progressively deteriorated until it no longer met regulatory guidelines. The hospital, a publicly funded military facility, requested funding to repair the ventilation system, but funds were not forthcoming because of budget austerity. When an increase in infections was documented, high-risk operations were curtailed and funding was expedited. With the new improved ventilation system the operating rooms once again met regulatory guidelines and infections returned to baseline rates. Throughout the period infections remained below recognized national levels.

New Swedish occupational standards for some organic solvents

In 1987, the Swedish government requested a unique investigation of the consequences of a 50% reduction of permissible exposure levels (PEL) for organic solvents. As a result, 29 solvents were investigated and for 25 of them a reduction--if not to 50%--was suggested. For 13 of the solvents, there existed scientific arguments for a reduction of the PEL. For 12 solvents, no specific biomedical information was available. Presumed interactions between solvents may have influenced the decisions, but technological/economic feasibility criteria may also have been used by the regulators. This suggests that the use of technological/economic feasibility criteria can give lower PELs than health criteria. This is within the intentions of the Swedish Work Environment Act.