Fume and vapour emissions

In the food processing industry the concept of total contamination control is the main objective, and the same standards are being appUed as for the pharmaceuticals sector. 

Protection using low turbulence air flow permits germ-free air to move on parallel streamlines. The recommended velocity for vertical flow is 0.3 m/s, with 0.45 m/s recommended for horizontal flow. This is equivalent to an air flow rate of 1000-1500m / hr per m of room area - very much higher than typical air-conditioning systems. 

Generally, in the planning of a clean air protection scheme, it is important to limit the extension of the area protected with low turbulence displacement air flow to the absolute minimum, using the spot protection principle with restricted local use of displacement air flow, where it is feasible to do so. 

Section 6B has been almost entirely concerned with the filtration of air at the entry to a workspace or living zone. Equally important are the situations where a process is generating fumes, vapours and dusts, from which people hving or working in the neighbourhood must be protected. Fume and vapour emissions are covered in this chapter, mainly concerned with relatively low concentrations of contaminant, with dust collection in the next. Section 6D, where contaminant concentrations can be higher. 

Legislation places the onus firmly on the employer to be responsible for worker protection against fumes and vapours at the place of work. A European Union Directive, for example, formalizes an approach for worker protection in industry, which is embodied in a range of national regulations. 

---

There are at least six general methods of ventilating a working space. The first and simplest involves natural ventilation, where the room s doors and widows are left open. The advantage of this method is that there is no additional investment, but it does not directly solve any problem of fume or vapour emission on the premises, and there is a high heat loss in winter. 

The use of aqueous foams to control fume or vapour release from reactive chemicals is discussed. An acid-resistant foam NF2 controlled fume emission from 35% and 65% oleum, and from titanium tetrachloride, but was not effective for sulfur trioxide and chlorosulfuric acid. An alcohol-resistant foam NF1 suppressed ammonia vapour emission by 80%, and Universal fire foam reduced evaporation of ethylene oxide, vinyl chloride and methanethiol, and reduced vapour emission of 1,3-butadiene by 60%. Safety aspects of foam blanketing are discussed [1]. Equipment and application techniques are covered in some detail [2],... 

The emissions from heat treatment furnaces mainly comprise combustion gases, particularly from gas- and oil-fired furnaces. The composition of the combustion gases depends on the fiiel-t) e used. Oil-fired furnaces will generate S02-emission, which are not present for natural gas burners. Where quenching processes are carried out, emissions of fume, water vapour, or oil mist will also occur, depending on the quenching media. 

Most potential hazards of bitumen arise from handling the bitumen at elevated temperatures (more than 100°C). At elevated temperatures, skin burns and inhalation of vapour and fume emissions are the most common hazards that occur. However, there is always a danger associated with water coming into contact with hot bitumen and its self-ignition-combustion. 

A variety of vapours and fumes are emitted during handling bitumens at elevated temperatures. Visible emissions or fumes normally start to develop at approximately 150°C and the amount of fume generated doubles for each 10°C to 12°C increase in temperature (Shell Bitumen 2003). 

As in the case of dust emissions (Section 3.4), some localized containment of fume may be effected by exhaust ventilation (LEV), although for vapours the control achieved is by dilution (Section 4). Additionally for vapours there is the problem of knowing where to implement controls when there is no visual evidence of emission. The insight gained by studies of emission processes remains fundamental to the practical and effective control of volatile pollutants by any means. Investigations into the quality and quantity of post-vulcanization vapours occupy one priority area of current research effort. 

One benefit of the emerging understanding of vulcanization fume is an appreciation of the potential for controlling the release of a vapour from rubber. This is control at source in the stricter sense as previously applied (Section 3.4) to the control of dust generation from solid additives. Examples of the implementation of this approach to control specific component emissions include the removal of Nonox or NDPA from rubber formulations and their replacement by safer alternatives. Such control at source has been described in general terms as achievable in two ways. ... 

---