Is it mandatory to apply for exemption U/s-87 and 88 of ESIC Act for every employer whose workers working in non implemented area?

R/Sir, Please guide is it mandatory to apply for exemption U/s-87 and 88 of ESIC Act for every employer whose workers working in non implemented area, or is it voluntary.
If the contractor doing site work in non implemented area and his office in the implemented area then it is mandatory for him to apply for exemption U/s-87 and 88 for his employees employed in non implemented area.
Thanks

@SKBansal
if the workers are out of reach of hometown then the contractor must has got a registered address on site, ask for a ESIC sub code there, and maintain muster roll of the onsite employees, ESIC will inform the status and if it is out of coverage then they will not ask for contributions,
Keeping the members in HO muster roll will raise question mark of their deputation at "non implemented sites"

The ESI is not applicable to the contractor working in non implemented area.
The employees of the contractor establishment in the implemented area are covered under ESI, provided having 10 or more employees are enrolled.
If all the workman of the contractor has enrolled in the muster roll of the establishment are covered under ESI.
An application for exemption U/s-87 and 88 would not exempt your establishment.
It is therefore, keep the establishment muster roll strength below 10 in implemented area. And rest of manpower in non implemented area.