Thermo Scientific VT 6060 M-BL, Руководство по эксплуатации

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3. UNIT SPECIFICATION
OPERATING PRINCIPLE
The oven has been designed for general heating and vacuum applications. Equipped with special
safety devices, the oven is also suitable for the heat treatment of articles or materials that contain
or are coated with combustible solvents which release vapors that burn or produce a dangerous,
potentially explosive mixture when they come into contact with air.
Apart from the usual regulations and standards for explosion protection, other fundamental princi-
ples / knowledge must be referred to in order to assess the explosion hazard and derive the re-
sulting structural measures to be implemented.
At the beginning of the 1930s, various series of experiments and findings were published on the
subject of "combustion limits of combustible vapor/air mixtures in a vacuum". These experiments
showed that a solvent vapor/air mixture only becomes explosive when a certain
minimum pres-
sure prevails in the mixture.
For example, a mixture of ether vapor and air is only explosive when the pressure exceeds
approx. 200 mbar and a mixture of alcohol vapor and air requires a pressure in excess of approx.
400 mbar before it becomes explosive.
lt is generally accepted that an explosive mixture of solvent vapor and air can be ruled out with an
adequate degree of certainty at a pressure of approx. 0.1 bar.
If minimum pressure is under-
shot, this is a more or less a primary explosion protection measure.
An explosion with dangerous consequences can only occur when the following conditions are
fulfilled simultaneously:
1.
The concentration of the combustible substance in the air is within the explosion limits.
2.
There is a dangerous quantity of explosive atmosphere.
3.
The combustible substance demonstrates a high degree of dispersion (vapor, mist) in air.
4.
There is an effective ignition source.
An explosion with dangerous consequences cannot occur even if only one of these
conditions is not fulfilled.
The following protective mechanisms offer a solution to this problem without detrimentally, affect-
ing the working parameters any more than necessary (lowering the operating temperature, reduc-
ing the heating power, limiting the surface temperature, ...):

Implement suitable structural measures to ensure that the pressure in the chamber falls below the
minimum ignition pressure quickly once the process has started, before activating the "hot surface
- heating" potential ignition source.

The possibility of an increase in pressure in the event of a fault must be taken into consideration
(e.g. power failure, leakage, ...) during the process and the protective system raust be provided to
handle this situation.
The hot surfaces which are present when the oven is in service must be enabled by a monitored
system to ensure that explosion protection is still provided in the event of a fault in this facility.