A person shall not refuse or fail to render assistance in combating a forest, brush, or grass fire at the summons of the department, or its authorized agent who is charged with the prevention or suppression of fire or the enforcement of the state fire laws, or any county firewarden, fireman, or county officer who is charged with the duty of preventing or combating forest, brush, or grass fires, or any officer of a county fire protection district, unless prevented from so doing by sickness or physical disability.