6.4.1 Introduction

The need for exact target values relating to processes and products is self — evident in the design phase of process technology, equipment manufacture, and many other areas of engineering. Industrial ventilation is defined as “airflow technologies” to control the workplace indoor environment and emissions.” It is therefore logical that the goals of industrial ventilation are unambiguously quantified. In the past the design goals of industrial venti­lation have been expressed in many terms, such as airflow rates, filter classes, control velocity of a local exhaust hood, and surface temperature of a radiator. Although these are indispensable quantities in the design and realization processes, they account only indirectly for the environment within the premises. Therefore, the goal of industrial air quality should be defined using target values of the relevant contaminants occurring in the room.

The need for the implementation of target levels for air quality in indus­trial work rooms stems from different concerns. In addition to technological factors, the systematic design methodology, life cycle assessment, advances in air distribution methods, and increased integration with the process and

Building automation have to be considered. The recent changes in the stan­dards of working conditions that favor the target level process also must not be forgotten.

Occupational exposure limits (OELs) have been used for decades as expo­sure criteria for air contaminants (see Sections 5.3 and 6.2). OELs are quanti­tative health standards expressed as a maximum mean concentration of dangerous air contaminants over a given reference period. Although OELs are required for the establishment of health-based standards, the limits entail a great deal of uncertainty. They indicate the minimum level of air quality corre­sponding to the present understanding of what is an acceptable risk, but they do not serve as a criterion for planning a comfortable environment and con­trol technologies for the whole life cycle of the system, say over a period of 20 years.

Although high exposures to air contaminants still occur in a number of in­dustries, the general trend is that the current levels of most c >mmonly used chemicals are decreasing and are clearly lower than the correspi ndmj OELs. This means that more people are working in cleaner environments than previ­ously. In the 1990s a discussion began by industrial hygienists and associated work environment specialists on the role of the OELs and the system for set­ting the limits.1 There is the opinion that the OELs have less impact on the im­provement of occupational environment than in previous decades, and that they focus on compliance testing instead of control. It is also worth noting that compliance with the occupational exposure limits does not guarantee 100% protection for all individuals.

Nowadays many companies have adopted a policy of continuous im­provement of working conditions. Therefore, it is desirable to create target levels for those who want to pursue more efficient control by applying the best available control technologies. There are also endeavors to create optimal working conditions in order to improve the performance and the innovative­ness of a staff, and hence enhance productivity. A series of laboratory and case studies show that employee productivity is higher when the work environment is appropriate for the tasks being done.2 Such efforts are typical in the ad­vanced sector of industry. One can say that there is a transition from “blue — collar to white-collar work.”

Today occupants, building owners, and other end users of ventilation sys­tems are more interested in the level of air quality and thermal climate than in the techniques by which that level is achieved. This is supported by the fact that industrial ventilation systems in modern premises are more complicated and tightly integrated with the process and building automation. It is therefore difficult for end users or nonprofessionals to evaluate whether a ventilation system is functioning correctly.

The aim of this section is to consider the scientific and technological grounds for assessing target levels of contaminants that frequently occur in the occupational environment as well as use of the target levels. The target level (TL) of a contaminant is defined as the predetermined concentration of a dominant contaminant to be achieved by air technology or other con­trol methods. A target level can be considered for an entire room volume or a zone, such as an occupied zone or a limited part of the occupied zone.

Unlike OELs, the proposed target levels for air contaminants are voluntary guidelines.