Flammable solvents are increasingly being used as a substitute for halogenated hydrocarbons. For environmental and cost reasons, use of the solvents is optimised through treatment in small distillation plants for re-processing. A partial vacuum atmosphere prevails in these plants. The pressure-dependent safety parameters of the substances employed are still by and large unknown for the partial vacuum range, which means that there is no satisfactory factual basis for drawing up safety requirements. Goal: determining the pressure-dependency of the safety parameters in the partial vacuum range and the pressure limit values at which an explosion can be ruled out.
Determining parameters for the lower and upper explosion limit, flameproof opening, explosion pressure for stoichiometric mixtures of pure substances and representative substance mixtures (octane, isopropanol, n-undecane, propyleneglycolether, petrol mixture, zestron) at pressures between 100 and 1013 mbar and temperatures of 20 °C to 100 °C.
With decreasing pressure the lower explosion limit increases slightly to 400 mbar, and progressively below this figure; the decrease in the upper explosion limit with decreasing pressure is dependent upon the substance. At 20 °C explosions in mixtures are possible above 100 mbar, at 150 °C this is already possible at 20 mbar; the constant ratio Pmax/P is 9.5.
International Symposium on Loss prevention 1998. ACHEMA 97 PTB-Bericht (NN)
-cross sectoral-Type of hazard:
Lösungsmittel, Anlagensicherheit, Brand- und ExplosionsschutzDescription, key words:
A partial vacuum reduces the risk of explosion of flammable vapours, with higher temperatures, however, the vapour can explode until very low pressure is attained.