local exhaust ventilation

Open fronted ventilated enclosures are commonly used in industry to control worker exposure to a wide range of chemicals. These enclosures tend to be of basic design and often consist of nothing more than a box like structure with an open front to allow worker access and extraction at the rear to remove contaminated air. This design forces the worker to stand at the face of the enclosure and by doing so presents a blockage to the airflow.

Presents new empirical formulae for the prediction of the air velocity in front of rectangular (slot) openings. Infers the equations from an experimental study of a common type of local exhaust opening. The formulae describe the three-dimensional velocity field near a rectangular exhaust hood, providing the velocity gradients along suitable directions, parallel to the slot axis. Testing of the formulae showed a good fit to the experimental data.

Occupational hygiene conditions were examined in a welding shop after repairing the air-handling unit. Good indoor air quality was achieved with the new replacement ventilation system. The airborne dust concentrations varied from the detection limit of 0.1 mg/m3 to 0.8 mg/m3 at the stationary sites. Even the breathing zone concentrations of the welders remained below or equal to 2.1 mg/m3. The concentrations of carbon monoxide did not exceed the level of 1 cm3/m3.

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.

In North America, there is an ongoing effort to repair the effects of corrosion in large boilers and pressure vessels. In recent years this work has been done from scaffolds erected in the boiler or vessel. The largest pressure vessels in British Columbia are known as Kamyr Digesters, and are found in Kraft pulp mills. The boilers are found in pulp mills across Canada and the USA, and in thermal power plants in east of the Rocky Mountains in Canada and across the USA. The scaffold structures are made up from 50 mm diameter steel columns and struts that are assembled with steel wedges.

Although the REEXS-principle Reinforced Exhaust System) has been the object of numerous investigations, who found substantial improvements compared to ordinary local exhaust ventilation hoods, it is far from being generally accepted and used. A Swiss team consisting of researchers of the ETHZ (Swiss federal institute of technology), the EMPA (Swiss Federal Laboratories for Materials Testing and Research) and the company Sulzer Infra have started a project for further investigations of REEXS hoods in the frame of the COST G3 action Industrial Ventilation.