values to calculate the assimilation of harmful gases and vapors
Values regulated by the SN 245-63. When released, only one harmful gas, the calculation is at its assimilation. In the case of the selection of several harmful gases and the amount of ventilation air is taken for the hazard, which requires the most with the exception of the joint allocation of the following hazards:
a) several solvents (acetone, alcohols, esters of acetic acid, etc.);
b) several irritant gases (sulfur and sulfur dioxide, hydrogen chloride, hydrogen fluoride, chlorine, etc.):
c) nitrogen oxides with carbon monoxide.
In these cases, the number of required air is calculated for each hazard separately, and received volumes of air are added.
If the hazard is uniformly distributed around the room and the allocation of them would be unchanged by time, the coefficient r would be equal to 1 and the above formula (30) could lay claim to accuracy. In fact, uniformity, peak in the first or second case is not observed. Directly from the source selection harm its concentration can be many times higher than the average - the maximum allowable. A few meters from the source concentration, in contrast, can be much lower, down to zero. On the other hand, in the presence of powerful heat flows gas hazard shall be put out of work area and gather at the ceiling, from which usually are removed. When artificial mixing, for example when applying a concentrated flow, the concentration of harmful substances more aligned with that, however, does not exclude the presence of separate zones of increased or decreased concentration.
As a rule, the hazards are allocated unevenly over time. The most striking example of this irregularity are gassing from cars in garages and random-gassing of the leaks, test cocks, etc. The same can be said about drying and evaporation in the painting, about the gassing in foundries and the many other cases.
Gases, vapors and aerosols in concentrations not exceeding the limits can be transported long man without harmful effects. However, inhalation hazards, even in small concentrations is not good for health. In terms of health it is advisable that people at least part of his working time was in pure air. Hence the tendency - to provide parameters hazardous industries restrooms, air oasis, etc.
From these considerations, undesirable mixing of the air pollution hazard lumped air-supply jets. In fact, if thoroughly mixed the air in the shop and to achieve overall maximum permissible concentration of harmful substances, it is nowhere left corner, which would be "free" to breathe. In other words, all workers would be equally bad for the entire shift.