Whenever in the opinion of the Office the amount of security given by the self-insurer is insufficient to afford adequate security for the payment of benefits and medical expenses under the Act, the self-insurer shall, upon demand by the Office, file such additional security as the Office may require. The Office may reduce the amount of security at any time on its own initiative, or upon the application of a self-insurer, when it believes the facts warrant a reduction. A self-insurer seeking a reduction shall furnish such information as the Office may request relative to his current affairs, the nature and hazard of the work of his employees, the amount of the payroll of his employees engaged in coal mine employment within the purview of the Act, his financial condition, and such other evidence as may be deemed material, including a record of benefit payments he has made.