Quantitative and qualitative gas analysis is widely needed in present modern industrialized societies. The reasons for this need range from purely economical interests, to meeting the requirements of environmental and occupational health legislation. Examples of these applications include process effluent monitoring, emission monitoring, workplace safety monitoring, clinical blood gas monitoring, toxic gas monitoring in fires, chemical warfare agent detection and ambient air monitoring.

The presence of airborne contaminants in the production environment can create problems to products, production equipment and personnel. The improvement of the production environment is a complex task and therefore, unprofitable control measures are common. PIMEX and similar equipment (1-6) combines video picture of the work and simultaneously measured data from the sensors detecting e.g. airborne contaminants. Link between problem calling conditions and work can be analysed with the aid of video picture in which graphical presentation of data is superimposed.

The performance of an exterior hood is known to be affected by the cross draft (1, 2). Based on the knowledge from a classical "Rankin's nose" or "semi-infinite body" problem, in which the opening shrinks to a sink instead of a finite opening, the exhausted airflow combining the cross draft forms a capture envelope in front of the hood(3). All streamlines within the envelope lead to the hood opening, those outside of the envelope lead to infinity. Therefore, contaminant released inside the envelope tends to be captured by the hood; otherwise, it tends to escape beyond capture.

Standard design methods for local exhaust hood design require the selection of the necessary capture velocity and then application of empirical equations relating capture velocity with hood flow rate. The selection of capture velocity depends on hood geometry, source generation rate, and disturbances in the vicinity of the local exhaust hood. Current design techniques for vapor degreasers require a hood flow rate of 0.25m3s-1 per m2 of tank area.(1) The design method does not account quantitatively for crossdrafts, but instead recommends eliminating crossdrafts.

In the printing office the use of dyes and solvents often results in occupational health problems. Today, target levels for industrial air quality and acceptable worker exposure are much lower than before. This makes heavy demands on the exhaust efficiency of polluting processes as well as it focuses on worker exposure. This paper describes a process of optimisation of exhaust efficiency and of minimisation of worker exposure at a semiautomatic printing machine at a printing office.

Ventilation systems can be divided in many ways, by size, flow rate, velocity, material, placing, aim, etc. One common way is to divide between General Ventilation (GV) and Local Ventilation (LV). However, these terms do not have general accepted meanings. In the Design Guide Book for Industrial Ventilation (DGB), chapter 10 Local Ventilation, we (members of COST G3 Working Group 4) have tried to define and describe Local Ventilation systems. We have also made a division of L V into different specific systems.