What is meant by 'compulsory insurance' under the Public Liability Insurance Act, 1991?

Section 4 Public Liability Insurance Act, 1991 deals with compulsory insurance. It requires the owner to take out one or more insurance policies, before starting the handling of hazardous substance. Such insurance policy should provide for contract of insurance, whereby he is insured against liability to give relief under Section 3(1) of the Act. The amount of insurance policy should not be less than the amount of paid up capital of the undertaking handling any hazardous substance and more than the amount, not exceeding rupees fifty crore, as may be prescribed.