Determination of hazard to air exhausted
Defining the air when general ventilation should be established, whether the work proceeds engine more or less evenly over the estimated hours (say, 5 times for 2 min), or "concentration" (10 min for 1 h, the engine runs, and 50 min did not works). In the latter case, the concentration of carbon monoxide will be significantly changed by the time that must be borne in mind when determining the amount of air extracted from the premises.
In existing facilities is sometimes defined amount of gas or vapor entering the room, on the basis of chemical analysis of air. At inspection department in conjunction with analysis of air in the room air is measured both artificial and natural.
The required amount of pollutant entering the space defined by the formula
G = V (k2 - k1) (g / h)
where V - the room in cubic m3;
k1 and k2 - the final and initial (before the survey), the concentration of fumes or gases in the air space in g/m3;
L - value of air in the room in m3 / h; VA, etc - the average concentration of vapor or gas removed, and the supply air in g/m3; z - the test in hours Here is an example of such a calculation.
In the premises inspected by a variety of sources released an aerosol of sulfuric acid. Mechanical ventilation with a multiplicity of exchange equal to 12. Number of exhaust air is 12 000 m3 / h. The cubic capacity of 1000 m3 of space. The test was conducted for 3 h. The data analysis following air:
kt = 0,008 g/m3; kx = 0,002 g/m3; kWA = 0,01 g/cm3;
Cr = o
In this case, the air in the supply of sulfuric acid does not contain:
G - 1000 (0.008 - 0.002) 12 000 (0.01 - 0) 3 g / h
As can be seen, with intensive ventilation first term in the numerator of (26) almost does not matter to him can not be ignored. When the multiplicities of exchange equal to 1-2, the contents of hazard in the indoor air before the test and after it must be taken into account.
Determine the concentration of harm in the exhaust air during mechanical ventilation is comparatively easy. It is much more difficult for natural ventilation. In the latter case is also difficult to determine the air.
To gas hazards and aerosols close abut the so-called "hollow droplets and mist. In some cases, the fog is the result of selection of hollow droplets.
A classic example of selection of hollow droplets is electrolysis in aqueous solutions. Gas bubbles are enveloped by a liquid film and act in the air in the form of miniature balloons. In the future bubbles burst, forming a tiny spray of liquid - fog. Thus, in the premises for recharging the batteries in the absence of ventilation can be seen the mist of sulfuric acid, formed from hollow drops.