A method for determining the heat transfer and water vapour permeability of patient support systems.

The formation of pressure ulcers can be exacerbated by a breakdown in the integrity of the patient's skin caused by poor maintenance of the skin microclimate. Patient support systems (PSSs-specialised beds, mattresses, chairs, cushions and pads) play an important role in the dissipation of heat and moisture away from the skin/support interface which is necessary in order to maintain the physiological skin microclimate. This paper reports a laboratory method and theory for the simultaneous measurement of the heat and water vapour dissipating properties of PSSs. The results demonstrate that the method is extremely selective, exhibiting very significant differences between the PSSs tested. It also shows that assessing PSS covers independently does not necessarily indicate the overall performance of the complete PSS.

Computational fluid dynamics as a method for assessing fume cupboard performance.

A commercially available computational fluid dynamic (CFD) software program, specific for HVAC systems, was used to study the performance of an aerodynamic fume cupboard. The numerical results showed good qualitative agreement with physical measurements giving confidence in the CFD model to simulate and predict overall fume cupboard performance. However, there were some quantitative differences specifically around 'aerodynamic' features that could not be accurately simulated by the software code. The CFD model was clearly able to demonstrate differences in performance between good and bad cupboard designs, and show the importance of using rear baffles and lipfoils. It also showed the importance of good design features when a 'worker' was standing against the front edge or when there were draughts in front of the aperture. The computer model was used to simulate the gas tracer containment test method described in BS 7258 (1994) [Laboratory Fume Cupboards], and had a much greater sensitivity than the recommended physical measuring instruments. The results given in this paper demonstrate the potential for using a commercially available software package for the optimisation of fume cupboard design and testing. It also indicates the economy of using CFD compared with building a prototype and testing a model.

A simple method for fume cupboard performance assessment.

The performance of a fume cupboard is determined by a complex interaction of factors which are time consuming and expensive to determine. This paper describes a simple and practical means of ranking, and assessing fume cupboard installations that can help to discharge managerial responsibility for a 'safe' environment. The method also gives an economically viable and technically defensible system for assessing fume cupboard performance as part of upgrading exercises or performance audits. The assessment strategy uses flow visualisation techniques and measurements of inflow air velocity as well as overall condition evaluation to rank performance and identify poor performing cupboards. The method has been used to carry out a condition and performance survey of 199 fume cupboards, both aerodynamic and box-type designs, in an academic institution. The results of this survey are presented which not only highlight performance characteristics but also provide insights into user attitudes and knowledge of fume cupboard operation and performance. It is suggested that surveys such as this could be helpful in training programmes for laboratory workers to enable them to optimise the use of fume cupboards.