John E. Brockmann

Evaluation of a Wipe Surface Sample Method for Collection of Bacillus Spores from Nonporous Surfaces

ABSTRACT Polyester-rayon blend wipes were evaluated for efficiency of extraction and recovery of powdered Bacillus atrophaeus spores from stainless steel and painted wallboard surfaces. Method limits of detection were also estimated for both surfaces. The observed mean efficiency of polyester-rayon blend wipe recovery from stainless steel was 0.35 with a standard deviation of ±0.12, and for painted wallboard it was 0.29 with a standard deviation of ±0.15. Evaluation of a sonication extraction method for the polyester-rayon blend wipes produced a mean extraction efficiency of 0.93 with a standard deviation of ±0.09. Wipe recovery quantitative limits of detection were estimated at 90 CFU per unit of stainless steel sample area and 105 CFU per unit of painted wallboard sample area. The method recovery efficiency and limits of detection established in this work provide useful guidance for the planning of incident response environmental sampling following the release of a biological agent such as Bacillus anthracis.

Evaluation of rayon swab surface sample collection method for Bacillus spores from nonporous surfaces

Aim:  To evaluate US Centers for Disease Control and Prevention recommended swab surface sample collection method for recovery efficiency and limit of detection for powdered Bacillus spores from nonporous surfaces.

APS Response to Nonspherical Particles and Experimental Determination of Dynamic Shape Factor

A method to determine the dynamic shape factor of an aerosol from cascade impactor and aerodynamic particle sizer (APS) distribution measurements is presented and demonstrated. The response of the TSI, Inc., APS to nonspherical, porous particles is derived after the fashion of Wang and John. This method does not require microscopy or chemical analytical techniques and as such is an improvement over previous methods. *This work was supported by the U. S. Nuclear Regulatory Commission and was performed at Sandia National Laboratories, which is operated for the U.S. Department of Energy under Contract Number DE-AC04-76DP00789.

Evaluation of vacuum filter sock surface sample collection method for Bacillus spores from porous and non-porous surfaces

Vacuum filter socks were evaluated for recovery efficiency of powdered Bacillus atrophaeus spores from two non-porous surfaces, stainless steel and painted wallboard and two porous surfaces, carpet and bare concrete. Two surface coupons were positioned side-by-side and seeded with aerosolized Bacillus atrophaeus spores. One of the surfaces, a stainless steel reference coupon, was sized to fit into a sample vial for direct spore removal, while the other surface, a sample surface coupon, was sized for a vacuum collection application. Deposited spore material was directly removed from the reference coupon surface and cultured for enumeration of colony forming units (CFU), while deposited spore material was collected from the sample coupon using the vacuum filter sock method, extracted by sonication and cultured for enumeration. Recovery efficiency, which is a measure of overall transfer effectiveness from the surface to culture, was calculated as the number of CFU enumerated from the filter sock sample per unit area relative to the number of CFU enumerated from the co-located reference coupon per unit area. The observed mean filter sock recovery efficiency from stainless steel was 0.29 (SD = 0.14, n = 36), from painted wallboard was 0.25 (SD = 0.15, n = 36), from carpet was 0.28 (SD = 0.13, n = 40) and from bare concrete was 0.19 (SD = 0.14, n = 44). Vacuum filter sock recovery quantitative limits of detection were estimated at 105 CFU m(-2) from stainless steel and carpet, 120 CFU m(-2) from painted wallboard and 160 CFU m(-2) from bare concrete. The method recovery efficiency and limits of detection established in this work provide useful guidance for the planning of incident response environmental sampling for biological agents such as Bacillus anthracis.

An experimental and numerical study of particle nucleation and growth during low-pressure thermal decomposition of silane

This paper discusses an experimental and numerical study of the nucleation and growth of particles during low-pressure (∼1:0 Torr) thermal decomposition of silane (SiH4). A Particle Beam Mass Spectrometer was used to measure particle size distributions in a parallel-plate showerhead-type semiconductor reactor. An aerosol d ynamics moment-type formulation coupledwith a chemically reacting 8uid8ow mod el was usedto predict particle concentration, size, and transport in the reactor. Particle nucleation kinetics via a sequence of chemical clustering reactions among silicon hydride molecular clusters, growth by heterogeneous chemical reactions on particle surfaces andcoagulation, andtransport by convection, d i:usion, andthermophoresis were included in the model. The e:ect of pressure, temperature, 8ow residence time, carrier gas, and silane concentration were examined under conditions typically used for low-pressure (∼1 Torr) thermal chemical vapor deposition of polysilicon. The numerical simulations predict that several pathways involving linear and polycyclic silicon hydride molecules result in formation of particle “nuclei,” which subsequently grow by heterogeneous reactions on the particle surfaces. The model is in good agreement with observations for the pressure andtemperature at which particle formation begins, particle sizes andgrowth rates, andrelative particle concentrations at various process conditions. A simpli=ed, computationally inexpensive, quasi-coupled modeling approach is suggested as an engineering tool for process equipment design and contamination control during low-pressure thermal silicon deposition. ? 2003 Elsevier Science Ltd. All rights reserved.

Stage Response Calibration of the Mark III and Marple Personal Cascade Impactors

Experimental and correlated stage responses (the fraction of particles entering an impactor that are collected on a stage) are presented for the Andersen Mark III and Marple personal cascade impactors. The impactors were operated upright and fully assembled so that interstage interference and wall losses could be properly studied. The observed stage responses showed maxima that fell significantly short of unity, meaning that a monodisperse aerosol is never collected exclusively on one stage, but is distributed among several stages and internal losses. Correlations for the stage responses are presented so that the experimental results can be used to determine size distributions with available data-inversion algorithms. Simulations with log-normal distributions show significant differences between dpa50 histograms and the more accurate distributions that result by taking the response functions into account.

A Method To Employ the Aerodynamic Particle Sizer Factory Calibration Under Different Operating Conditions

The dimensionless aerodynamic particle sizer (APS) response function (normalized particle velocity against particle Stokes number) first reported by Chen et al. (1985) is explored for much larger solid particles (diameters to 35 μm) over a similar range of instrument pressures (624–l740 mm Hg) and flow rates (4.2–6.0 L/min). An essentially unique response function is found for low and intermediate Stokes numbers under a variety of operating conditions, including the use of argon as the carrier gas. For large particles, however, non-Stokesian drag effects introduce systematic differences among calibration sets so that a unique response function no longer applies. The largest differences are observed between calibrations performed in air and argon, although even in this case the sizing error amounts to < 12% for a 20-μm polystyrene latex sphere. For intermediate Stokes numbers, a direct consequence of this work is that a reference calibration (channel number against Stokes number) can be used under differen...

Calibration of the Aerodynamic Particle Sizer 3310 (APS-3310) with Polystyrene Latex Monodisperse Spheres and Oleic Acid Monodisperse Particles

We have calibrated the new, extended-range aerodynamic particle sizer (model APS-3310, TSI, Inc.) with polystyrene latex monodisperse spheres and compared the response to that of oleic acid monodisperse particles from 2.5 to 38.7 μm in diameter. The results compare well with previous findings and cover a larger size range permitted by the new instrument.

Experimental study of impulse resuspension with laser Doppler vibrometry.

Particle resuspension due to mechanical impulse was studied for spherical polymethylmethacrylate (pmma) particles ranging from 1.7 to 14.4 μm in diameter on titanium dioxide (TiO2) and silicon dioxide (SiO2) wafers. Dry powders were dispersed, electrostatically neutralized, and allowed to deposit under the influence of gravity. Contaminated surfaces were then mechanically excited with a 5 MHz piezoelectric transducer where surface accelerations (∼106 m/s2) and resuspension ratios were quantified with laser Doppler vibrometry (LDV) and digital microscopy, respectively. For TiO2, experiments were performed over a broad range of relative humidity (25 to 95%) to assess the effects of capillary condensation. Resuspension was a monotonically decreasing function of relative humidity. Existing theories were used to separate data into two adhesion regimes based on capillary bridge formation: van der Waals (vdW) and capillary dominated adhesion. For relative humidity above 60%, resuspension forces were nondimensionalized by the theoretical capillary force. Resuspension data for all particle sizes and relative humidity were described by a single sigmoid function dependent on the dimensionless resuspension force. Below 60% relative humidity, resuspension forces were nondimensionalized by the vdW force calculated with Johnson–Kendall–Roberts adhesion theory. The experimental work of adhesion (pmma-TiO2) was optimized such that the dimensionless resuspension curves, for capillary and vdW forces, had equivalent dimensionless resuspension forces at 50% resuspension. The calculated value, 0.047 J/m2, was within the range of values expected from other published works. Resuspension was not observed for particles on SiO2 substrates. This result was attributed to electrostatic surface charge patches where particle charge and surface resistivities were measured to analyze the relative influence of electrostatic adhesion forces. Copyright 2012 American Association for Aerosol Research

Effluent treatment options for nuclear thermal propulsion system ground tests

A variety of approaches for handling effluent from nuclear thermal propulsion system ground tests in an environmentally acceptable manner are discussed. The functional requirements of effluent treatment are defined and concept options are presented within the framework of these requirements. System concepts differ primarily in the choice of fission‐product retention and waste handling concepts. The concept options considered range from closed cycle (venting the exhaust to a closed volume or recirculating the hydrogen in a closed loop) to open cycle (real time processing and venting of the effluent). This paper reviews the strengths and weaknesses of different methods to handle effluent from nuclear thermal propulsion system ground tests.