Numerical and experimental analysis of airborne particles control in an operating theater

The design of a ventilation system for operating theaters (OT) is aimed to reduce the patient infection risk while maintaining adequate comfort and productivity for the surgical staff. Nowadays, Computational Fluid Dynamics (CFD) represents an important tool to simulate the airflow pattern in an operating theater and its ability to remove airborne particles. The CFD advantages, compared to experimental campaigns, consist in the ability to test different configurations, in the ease of implementation and in time and money savings. The aim of this work is to numerically and experimentally investigate an OT with a layout according to the Standard DIN 1946-4. Moreover the effectiveness of a differential airflow diffusion system on reducing the particle concentration above the operating table is analyzed. The supply air comes from a ceiling filter system composed of 23 H14 filters, which assures an unidirectional flow with differential air velocities over the protected area. In order to experimentally evaluate the performance and the protection grade SG, according to DIN 1946-4, and to validate the numerical results, a measuring campaign has been carried out within a laboratory setup of an OT. Two different scenarios have been adopted to evaluate the protection level against the entry of external and internal contaminant loads into the protected area. For both cases, the simulated and measured particle concentration in the protected area agree well, and the differential air flow diffusion system is able to maintain the desired protective effect (SG) against contamination load in both the design and the off-design conditions

On field ventilation performance in operating theaters against airborne contamination: a comparison of unidirectional and mixed airflow systems

Controversy exists between engineers and clinicians over the beneficial effects of Uni-Directional Flow (laminar airflow) adoption in the ventilation in the OR in order to further minimize airborne Surgical Site Infections (SSIs). This paper presents the results obtained during environmental monitoring campaign on 31 operating theaters (OTs), 18 OTs equipped with unidirectional air flow systems and 13 OTs adopted a mixing (turbulent) airflow ventilation system. Inert and viable airborne particle concentration have been measured in “at rest” and “operational condition” in different places within the OTs under evaluation. Number of persons present during operations, type of technical clothing system adopted, thermo-hygrometric conditions have been acquired as well as airflow rate, air velocity and type of filtration system. Results have shown how OTs equipped with unidirectional airflow diffusion system have generally lower inert and viable airborne particle concentration within the OT than those with mixed airflow, and therefore lower risk of SSIs

Single stage centrifugal air sampler: a theoretical and experimental approach for cut-off size (d50) evaluation

This work focuses on the study of the particle sampling efficiency of a small single stage centrifugal air sampler under different air sampling flow rates and particles diameters. The centrifugal force perpendicular to the mean airflow motion within the circular cavity is opposed to the viscous one, which depends on the particle aerodynamic diameter. The particles hitting the outer surface of the sampler stick on it and are trapped. Experimental tests have been done for the lowest particle size sampled by the instrument, usually called d 50 or cut-off size, at different air sampling flow rates. Experimental results for particle´s diameters higher than 2 µm agree quite well with those obtained by the theoretical model and by computational fluid dynamics simulations. Furthermore, it has been shown how the particles sampling efficiency of the instrument increases with the airflow rate

Dispersal chambers used for evaluation of cleanroom and surgical clothing systems - Examples of performed tests and results

Chalmers University of Technology in Sweden and Politecnico di Milano in Italy have developed and installed two experimental dispersal chambers (body-box) for the measurement of the rate of total and microbial airborne particle dispersion from persons (wearing technical clothing system) and from equipment in cleanrooms and in Operating Theaters (OT). This paper describes the two dispersal chambers and the adopted test procedures for person particle dispersion tests. The release rate of total airborne particles (in defined particle size ranges) emitted from a person and his gowning system while performing standard movements and the release rate of aerobic Colony Forming Unit (CFU) of the same person and gowning system, can be considered as the personnel source strength, a fundamental parameter both in design and in operation of a clean space. Moreover, the personnel source strength data could be used in order to compare technical clothing systems in terms of their particle shedding, and even more interestingly in terms of their ability to filter and to limit the personnel airborne particle release. The study presents data obtained in experimental campaigns made in the two labs. The results of the experimental tests carried out on different technical clothing systems are discussed and compared, highlighting the effect on emission rates of the garment type and of the number of undergone cycles of Washing, Drying and Sterilization (WDS). The source strength data presented in this paper can be used in the design phase of cleanrooms and of OT to size the total air flow required or contamination control and to forecast the concentrations of aerobic CFUs and total airborne particles

Some aspects on the sampling efficiency of microbial impaction air samplers

Indoor microbial monitoring is an important health issue in many sectors of society. In particular, it is important to monitor microbial concentrations in environments dealing with bio-susceptible products. Many human diseases are related to high, undesired microbial airborne concentrations. However, the lack of a standardized and well-accepted methodology for testing and ranking the performance of microbial air samplers is a source of uncertainty in such measurements. Several works clearly show that results obtained from microbial air sampling depend largely on measuring techniques, especially the air samplers\u27 physical parameters, such as d(50), as well as environmental conditions, sources, and concentrations of microbial organisms in the environment. Furthermore, personnel using cleanroom clothing can reduce the microbial burden within a clean environment. To evaluate this effect, we carried out experimental comparison tests in a cleanroom of class ISO 5 with different air samplers under various microbial concentration levels, generated by a human source dressed in different quality cleanroom clothing. Our results confirm that in addition to the measuring technique, cleanroom clothing does influence microbial contamination, affecting air sampler measurements

Performance test of technical cleanroom clothing systems

The work presented in this paper deals with aseptic cleanroom clothing systems performance and gowning procedures. The study had the purpose of evaluating the inert and viable airborne particle concentration shed by personnel when gowning a complete cleanroom clothing system suitable for aseptic operations at different washing, drying, sterilization (WDS) cycles. The tests procedure consisted of a normal working activity carried out in a stainless steel body box test rig. Inert and viable airborne contamination has been monitored continuously and in parallel throughout all experimental tests following aseptic procedures during the sampling task. Results have shown how WDS cycles, clothing size and personnel activity may influence the particle content shed by personnel and therefore the air cleanliness of an environment. Personnel working in clean environments might be aware of the importance of gowning system clothing and their procedures as well as the importance of training in operational behaviors in aseptic environments