Section 45 in The Factories Act, 1948
45. First-aid appliances.
(1) There shall in every factory be provided and maintained so as to be readily accessible during all working hours first-aid boxes or cupboards equipped with the prescribed contents. The number of such boxes or cupboards to be provided and maintained shall not be less than one for every one hundred and fifty workers ordinarily employed at any one time in the factory.
(2) Nothing except the prescribed contents shall be kept in a first-aid box or cupboard.
(3) Each first-aid box or cupboard shall be kept in the charge of a separate responsible person who holds a certificate in first-aid treatment recognized by the State Government and who shall always be readily available during the working hours of the factory.
(4) In every factory wherein more than five hundred workers are ordinarily employed, there shall be provided and maintained an ambulance room of the prescribed size, containing the prescribed equipment and in the charge of such medical and nursing staff as may be prescribed. These facilities shall always be made readily available during the working hours of the factory.
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Every state has additional rules as per the Factories Act. So kindly refer to your State Specific provisions also.