Toxicity released unhealthy
Estimated value of the velocity v is taken, depending on many factors, chief among them is the degree of toxicity of pollutant emitted, which determines the possibility or not a partial knockout hazards from the shelter. This is followed by the presence or absence of events, enabling ejection hazards. These include the phenomenon of mechanical, thermal, physical and chemical. A particularly important role played by thermal processes.
The proposed payment rate for shelters such as cabinets, enclosures, windows and canopies are summarized in Table. 12.
In determining the total area F for the shelters the most difficult to integrate all sorts of accidental leaks. Even in a stationary shelter for its good performance gaps are inevitable. In wooden shelters due to cracking and warping of the gap can be quite significant. Should consider the introduction of the looseness of a factor to the total area of all job openings and cracks.
Said ratio may be taken equal to:
for metal stationary shelters, depending on the availability of detachable joints and doors ............ 1 -1,2
for wooden stationary cover (in
Specifically, hoods )....... 1,2-1,4
for metal prefabricated shelters, depending on the frequency of dismantling shelters
and the number of detachable parts ...... 1,2-1,4
for wooden prefabricated shelters .... 1,4-1,0
For umbrellas, canopies at the door of dried, oven ostyvochnyh cameras, etc., which may release gases, the rate should be 1 m / sec.
For malovrednyh gas (with an allowable density of up to 10 mg/m3), the values given design speeds are somewhat too high and could be reduced by 30%. So, according to American practice, the rate shall be taken: for umbrellas without overhangs - 0,7 m / sec for umbrellas with two overhangs (open on two sides) -0.6 m / s, umbrella with three overhangs - 0,4 m / sec.
Umbrella of large sizes (for example, in the metallurgical industry), even at speeds in the horizontal section of 0.6 m / sec is obtained very significant amounts of exhausted air. If the umbrella has a size in terms of 6x2, 5 m, the amount of suction (F = 15 m2)
L = 3600 вЂў 15 вЂў 0,6 <32 000 m3 / h.
Regarding the veil, that when calculating the amount of exhausted air must be approached differently. Since the curtain less prone to "blowing" out from under them unhealthy, the speed in the horizontal section can be reduced even in comparison with large umbrellas.
At relatively harmless gases, vapors and aerosols may take the calculated air velocity in the horizontal section of 0,12-0,2 m / sec for large screens (20-30 m2) to 0,2-0,3 m / s for smaller screens sizes. When the toxic hazard curtains do not apply.