(3) The time spent by any person employed in a mine who is chosen for examination in the safety and occupational health survey, shall be counted towards his working time, so however that any overtime shall be paid at the ordinary rate of wages. Explanation.- For the purposes of this sub- section," ordinary rate of wages" means the basic wages plus any dearness allowance and underground allowance and compensation in cash including such compensation, if any, accruing through the free issue of food- grains and edible oils as persons employed in a mine may, for the time being, be entitled to, but does not include a bonus (other than a bonus given as incentive for production) or any compensation accruing through the provision of amenities such as free housing, free suplly of coal, medical and educational facilities, sickness allowance, supply of kerosene oil, baskets, tools and uniforms.