A. Cecala, D. Pollock, NIOSH, Pittsburgh, PA; A. O’Brien, Unimin Corporation, Winchester, VA; J. Howell, Unimin Corporation, Marston, NC.
A quick, safe, and effective process has been developed that allows workers to clean their dust laden work clothing periodically throughout the day. Contaminated work clothing has been a known major contributor to increased employee respirable dust exposure for many years. This newly designed process is relatively inexpensive and can be easily installed at any operation to allow workers to clean their clothing without contaminating the worker, the work environment, or co-workers to elevated respirable dust levels. This clothes cleaning process uses an air spray manifold to blow dust from a worker’s clothing in an enclosed booth. Since the booth is under negative pressure, no dust escapes to contaminate the work environment and or other workers. The worker performing the cleaning process is required to wear a half-mask fit-tested respirator, hearing protection, and full seal goggles. Dust samples taken inside the respirator of test personnel performing the clothes cleaning process showed very minimal to no respirable dust exposure. During field testing, the clothes cleaning process was 10 times faster (taking less than 20 seconds) and was approximately 50% more effective than either the federally approved method of vacuuming, or the most commonly used method of using a single air hose. This new process was developed under a cooperative research effort by National Institute for Occupational Safety and Health (NIOSH) and Unimin Corporation. This clothes cleaning process has tremendous applicable to any industry where workers’ clothing becomes contaminated with any type of dust or product.
R. Valladares, W. Sieber, J. Kratzer, CDC/NIOSH, Cincinnati, OH.
Respirable crystalline silica dust exposure in residential roofers is a recently recognized hazard resulting from cutting cement roofing tiles. Roofers, cutting tiles using masonry saws, can be exposed to high concentrations of respirable dust. Silica exposures remain a serious threat to nearly two million U.S. workers. Although it is well established that respiratory diseases associated with exposure to silica dust are preventable, they continue to occur and cause disability or death. The effectiveness of a commercially available local exhaust ventilation (LEV) system and a water suppression system to reduce silica exposures were evaluated separately. The LEV system exhausted 500 cubic feet per minute (CFM), while the water suppression system supplied two gallons per minute (GPM) to the saw blade. Using a randomized block design, implemented under laboratory conditions, three trials were conducted (no control, water control, and ventilation control) on two types of cement roofing tiles using the same saw. Each treatment was replicated for a total of eight 30-sec runs per treatment per tile. Analysis of variance was performed using mean concentration levels from each run and control. The use of water controls and ventilation controls resulted in a statistically significant (p < 0.05) reduction of mean respirable dust concentrations for each tile. Mean concentrations using the water control were statistically significantly less than that of the ventilation control. The percentage reduction for respirable dust concentrations was 99% for the water control and 91% for the LEV. Water is a good method for reducing crystalline silica exposures. However, water source and disposal requirements, water damage potential, surface discolorations, material expansion, cleanup, and other requirements make use of water in many situations problematic. LEV may be more desirable, but designing a system with a sufficient capture velocity that will control silica concentrations below occupational criteria might be difficult.
T. Rimmer, University of Arkansas for Medical Sciences, Little Rock, AR; S. Yarnell, Pactiv Corporation, Fresno, CA.
Occupational exposure to carbon monoxide (CO) from liquefied petroleum gas (LPG) powered forklifts is a common concern in warehouse operations. Engine tune-ups of five LPG forklift engines utilizing an exhaust gas probe with CO detection based on either colorimetric tubes or a nondispersive infrared detector were found to be effective in reducing the exhaust concentration from a mean value of 5.0% (range 3.0 to 7.0%) to a mean of 0.82% (range 0.7 to 0.9%). However, the tune-up process utilizing detector tubes was found to be too time consuming to be practical, leaving the use of the infrared instrument as the only viable alternative. As an evaluation of the effect of the emission reduction on warehouse personnel exposures, breathing zone and area CO measurements were made before and after the tune-up process in a large warehouse with no mechanical ventilation. For forklift operator and trailer loading helpers, the observed full-shift time-weighted-average mean reduction was 65% (27.8 ppm to 9.8 ppm, n = 5). Area sample concentrations showed a similar mean reduction of 54% (14.2 ppm to 6.5 ppm, n = 6). Although the environmental concentration reductions were both practically and statistically significant, they were less than the observed mean exhaust gas concentration reduction of 84%.
E. Hudson, Fluke Corporation, Everett, WA.
Air quality instruments depend on precise, complex and sometimes delicate electronic and mechanical systems. They must operate in changing and challenging environments, yet deliver consistently accurate results. Instrument performance affects the results achieved by the air quality professional and results are directly linked to reputation. Without the ability to measure air quality factors accurately and link measurements to known standards, one may as well hold a wet finger in the air. Yet air quality instruments vary in their inherent accuracy, in the range of environmental conditions in which they stay ‘in spec,’ and in their stability over time. To be confident in their tools and the data they produce, air quality professionals need to understand:
IAQ professionals can resolve issues of instrument performance by considering these issues when choosing, operating and maintaining instruments.
Conclusion: By understanding the factors that influence instrument performance, choosing instruments carefully, and maintaining them correctly, IAQ professionals can ensure themselves and their employers of accurate data and effective air quality remediation.
S. Rucker, G. Smith, H.C. Nutting Company, Cincinnati, OH.
After installation and fit-up of eleven new air-handling units (AHUs) for a 500,000 SF addition for a major metropolitan hospital, double walled panels of galvanized steel were corroding and insulation inside the panels was water soaked. These conditions prompted an assessment of causation and indoor air quality. Manufacture’s representatives recommended replacement of damaged panels without determination of cause. Panel replacement was time consuming and expensive with no assurance of finding all the damage. Is this corrective action appropriate for a health care facility who will assume responsible for equipment maintenance? The failure to identify the source of water and corrosion prevented accurate estimates of maintenance costs. In addition, areas of microscopic damage may have gone undetected, but could become a future problem. At a cost of between $1,200 and $2,500 per ton, a 50-ton AHU is approximately $90,000. Annual preventative maintenance (PM), inclusive of filter changes and belts, can be estimated at 10% of initial costs. Electric operational costs, assuming continuous operation, can be estimated at 20% of initial costs. These expense estimates do not include premature mechanical failure and emphasize the need to identify the source(s) of causation. The results of visual inspection were a useful indicator of exterior corrosion damage, but will fail to identify interstitial damaged inside double wall insulated panels. Drilling holes caused problems with warranty coverage. Thermal imaging was not useful.The options for confirmatory testing of problems with AHU panel assemblies are discussed. The application of tests such as G90 galvanizing, chemical assays of corrosive salts, and microbial induced corrosion are presented, including attributes and limitations. Findings from testing specialized materials are coupled with indoor airborne mold results and presented in a manner that illustrates the link between mechanical systems and indoor air quality.
C. Feigley, N. Schnaufer, T. Do, E. Lee, M. Venkatraman, J. Khan, University of South Carolina, Columbia, SC.
Various deterministic models have been used to estimate emission rates and emission factors. Here models were compared for estimating emission factors for isoamyl acetate (IAA) after dipping batches of capacitors to seal them. IAA concentrations were measured on three days with different production rates in the near-field and far-field using both charcoal tubes and diffusive samplers. Supply and exhaust air flowrates, and air speed and direction at various points near the source were measured as well. The two-zone model was selected as most applicable to the workroom studied and was adapted to improve the accuracy of emission rate estimates. This model’s standard formulation for concentration in the near field is: C = (G/Q) + (G/ß), where C is the near-field concentration, G is emission rate, Q is the flow of clean air into the workroom, and ß is the rate of air exchange between the near and far fields. G/Q, which represents the far field concentration, was replaced by the average measured concentration upwind of the source. Also, ß was calculated based on the average air speed toward the source and the cross-sectional area of the hemispherical near-field. The emission rates for the three days studied were: 1.5 x 10-2, 4.0 x 10-2 and 1.7 x 10-2 kg/hr corresponding to 10, 24, and 14 dips during the sampling period. Thus, the emission factors were 9.5 x 10-3, 13 x 10-3 and 9.1 x 10-3 kg/dip for an overall average of 10 x 10-3 kg/dip.
M. Scholler, Brno University of Technology, Brno, Czech Republic; P. Heiselberg, Aalborg University, Aalborg, Denmark.
High energy cost is the reason why houses with low energy consumption are being developed and built. The most important parameters which should be optimized to achieve a low energy house, are the wall heat transfer coefficient and efficiency of a ventilation system. Nowadays, the attention is drawn to hybrid ventilation systems, which are a good compromise between mechanical and natural ventilation systems. The paper deals with CFD simulation of efficiency of a hybrid ventilation system in a typical three bedroom apartment. The parameter which is monitored as the efficiency of the ventilation system in this case is CO2 level in the apartment. The recommended value that should not be exceeded is 1,000 ppm CO2 otherwise people who are in the apartment become tired. The main source of CO2 in the apartment is production of the people. Four people are assumed to be in the apartment in different locations and with different production of CO2 according to their activity (sitting or sleeping). Three day time variants and three night time variants are compared. Fresh air in the apartment is provided by inlet devices which are situated in each bedroom and in living room. Different air flow rate through the inlet devices in different variants is prescribed. Thermal comfort in the apartment is not discussed therefore simulated thermal conditions correspond with standard thermal conditions in residential buildings. The CFD model of the apartment was created and solved using the commercial code FLUENT.
Posted May 30, 2006