Section 11. The marshal may expend the amount annually appropriated for the employment of expert assistance, and also for maintaining a laboratory to aid in the enforcement of the laws relative to explosives and inflammable fluids and compounds. Expert assistants employed under this section shall aid in the enforcement of all laws, rules and regulations which it is the duty of the department to administer and enforce, and shall perform such other duties as the marshal may prescribe. Said expert assistants shall be exempt from chapter thirty-one and the rules and regulations made thereunder.