scope:

INTRODUCTION

Ventilation systems can be potential sources of pollutants due to the accumulation of dust in their air systems. Building managers have to consider a wide range of proposals from specialized cleaning companies and have difficulty arriving at a decision because there is no recognized or standardized method for assessing a system's dust contamination. Ventilation systems must therefore be maintained under optimal cleanliness conditions. For the optimal maintenance of facilities, it is important to be able to measure the amount of dust that has been deposited in ventilation networks. In all cases, an objective diagnosis avoids unnecessary network cleaning, but if decontamination is required, allows the cleaning methods to be chosen (ASPEC 2004).

In the United States and Canada, the initiation of air system cleaning is currently based on visual inspection (Lavoie and Lazure 1994; Brosseau et al. 2000). However, this is subjective and rather impractical for major cleaning work. In 2006, the American National Air Duct Cleaners Association (NADCA) published criteria for cleanliness acceptance after cleaning. However, these criteria are inadequate if you want to know when to start cleaning HVAC system networks (NADCA 2006). As well, these criteria can only be applied on rigid and non-porous surfaces, meaning smooth surfaces (e.g., metallic surfaces).

The Association pour la prévention et l'étude de la contamination (ASPEC, association for the prevention and study of contamination) in France has published a guide on methods for keeping the non-porous air systems of clean rooms and related controlled environments clean (ASPEC, 2004). In this guide, the initiation criteria for tertiary environments (office buildings) and the methods used are reported for different countries. Table 1 presents these criteria (ASPEC 2004).

This table shows that the criteria are accompanied by different dust sampling methods, thus making comparisons difficult. According to ASPEC, these methods can be applied only to rigid and non-porous ducts of sufficient dimensions, i.e., larger than 30 cm (11.8 inches) in diameter for round components; in addition, the ducts must be horizontal; and finally, the walls must be dry (ASPEC 2004). Sampling must be done on a layer of dust distributed on the bottom surface, and not on an accumulation of dust (ASPEC 2004). Furthermore, the sampling methods have some deficiencies, mainly the absorption of moisture from the air by the cellulose ester membranes, and the adhesion of dust on the walls of the cassettes and sampling tubes.

One method that would eliminate these two problems would involve weighing a complete sampling cassette such as the IOM cassette (SKC Inc. Eighty Four, PA, USA) equipped with a polyvinyl chloride membrane. However, this surface sampling method has not yet been evaluated. We will compare this cassette with the sampling systems mentioned in the literature in order to choose the most accurate method.

The objective of this project is therefore to propose a methodology for measuring the dust contamination of ducts in order to compare the numerical value to the value obtained from the visual evaluation corresponding to the limit value that determines the need for cleaning.