Whenever there shall occur an accident in which three or more employees of an employer insured with the state fund are fatally injured or sustain permanent total disability, the amount of total cost other than medical aid costs arising out of such accident that shall be charged to the account of the employer, shall be twice the average cost of the pension claims arising out of such accident. The entire cost of such accident, exclusive of medical aid costs, shall be charged against and defrayed by the catastrophe injury account.