Section 49B(5) in The West Bengal Factories Rules, 1958
(5)Safety ventilation. - (a) Every oven or drier shall be provided with positive and effective safety ventilation system using one or more motor-driven centrifugal fans so as to dilute, any mixture of air and any flammable substance that may be formed within the oven or drier and maintain the concentration of the flammable substance in the air a safe level of dilution.(b)The safe level of dilution referred to in clause (a) shall be such as to achieve a concentration of the concerned flammable substance in air of not more than 25 per cents of its lower explosive limit. Provided that a level of concentration in air upto 50 per cent of the lower explosive limit of the concerned flammable substance may be permitted to exist subject to installation and maintenance of an automatic device which(i)shows continuously the concentration of the flammable substance in the air present in the oven or drier at any instance.(ii)sounds and alarms when the concentration of the flammable substance in aft in any part of the oven or drier reaches a level of 50 per cent of its lower explosive limit; and(iii)shuts down the heating system of the oven or drier automatically when the concentration in air of flammable substance in any part of the oven or drier reaches a level of 60 per cent of its lower explosive limit and is provided to the oven or drier and maintained in efficient working condition.(c)No oven or drier shall be operated without its safety ventilation system working in an efficient manner.(d)No oven or drier shall be operated with a level of dilution more than what is referred to in clause (b) .(e)Exhaust ducts of safety ventilation system shall be so designed and placed as to discharge the mixture of air and flammable substance away from one workroom and not near windows or doors other openings from where the mixture may re-enter the workroom or create a pollution hazard in the neighbouring atmosphere.(f)The fresh air admitted into the oven or drier by means of the safety ventilation system shall be circulated adequately by means of circulating fan or fans through all parts of the oven or drier so as to ensure that there are no locations where the flammable substance can accumulate in the air or become pocketed to any dangerous degree.(g)Throttling dampers in any safety ventilation system shall be so designed by cutting away a portion of the damper or otherwise, that the system may handle at least the minimum ventilation rate required for safety they are set in their maximum throttling position.
