An accident happening to an emlpoyee in or about any premises at which he is for the time-being employed for the purpose of his employers trade or business shall be deemed to arise out of and in the course of his employment, if it happens while he is taking steps, on an actual or supposed emergency at those premises, to rescue, succour or protect persons who are, or are thought to be or possibly to be, injured or imperilled, or to avert or minimise serious damage to property.