total multiplicity of exchange
There are more refined data relating to chemical industries. If the height of the room up to 6 g or conditional zone up to 6 m is recommended following total multiplicity of exchange under the joint action of constant and emergency exhaust:
at the maximum allowable pollutant concentration of 5 mg/m3 and higher multiplicity of exchange no less than 8;
at the maximum allowable concentration of 3 mg/m3 and below the multiplicity of exchange no less than 12;
at the maximum allowable concentration of 1 mg/m3 or less the multiplicity of exchange no less than 16.
But such an approach to the appointment of the performance of emergency hood not justified.
The chemical industry is a permanent ventilation - aeration and mechanical general exchange with a local suction or mixed - is often a multiplicity of exchange, far in excess of 15 or 16. On the other hand, in big shops every now and even the creation of a 10-fold exchange requires a tremendous amount of air and is not justified.
As a first approximation, is proposed to determine the air at work emergency ventilation on the basis of the multiplicity of exchange, created a permanent ventilation.
The multiplicity of exchange created by the permanent ventilation through n. The total multiplicity of exchange are created by joint action of constant and emergency ventilation, denoted by m. Then
m = kn [r / h]. (76)
The value of k given in Table. 29.
For illustration we present some examples of calculation of the total multiplicity of exchange under the joint action is constantly running and emergency ventilation.
Inside ammonia compressor multiplicity of exchange is 3 on / hr Ammonia can form explosive mixtures with air. Allowable concentration of 20 mg/m3. Accept = 2,5. Then
T - 2,5-3 - 7,5 r / h.
Rules for regulating such premises for the multiplicity of the emergency ventilation for at least 7.
The shop is processed non-hazardous material with chlorine under pressure. Ventilation mixed, creating a multiplicity of exchange equal to 12. Emergency extraction is projected from the lower zone of the type of zonal suction. Allowable concentration of chlorine to 1 mg/m3. Given the zonal hood, take k = 2. Then
m = 2.12 = 24 rev / h.
In a small room with mixed ventilation possible emergency allocation of aerosols with the allowable concentration of 0.1 mg/m3. Multiplicity of exchange permanent ventilation is 22 rev / h. Take k = 2,5. Then
m = 2,5-22 = 55 rev / h.
In a large workshop of basic chemistry multiplicity of exchange permanent ventilation of 4 rev / h. Perhaps an emergency release of hydrogen chloride (permissible concentration of 5 mg/m3). Take k = 2. Then
m = 2-4 = 8 rev / h.
As can be seen, the multiplicity of exchange under the joint action of constant and emergency extraction obtained very different. They do not fit the norm of 7 to 15.
In the chemical industries, accompanied by the release of toxic substances with a permissible concentration of 5 mg/m3 n below, it is recommended to take measures to prevent hazards in located adjacent to municipal and administrative facilities. In the said premises shall be submitted with the influx of pressurization of at least 20%. Between the shop and mentioned premises should provide a gateway or vestibule, which can serve incoming air with a multiplicity of exchange is not less than 5 per hour.
The chemical industry time and again the atmosphere of the industrial site is contaminated process emissions. This phenomenon occurs due to insufficient cleaning process emissions of gases and dust or due to the impossibility itself. In this light it is interesting to mention about one fact.
Sanitary standards require cleaning ventilation air is emitted from the dust and gases.