240. Although the return to service of a retiring service personnel on invalid pension is not prohibited when he regains good health, that service personnel shall not be employed in the previous department if he was granted invalid pension on the medical certificate reporting that the incapacity of the service personnel was due to the conditions under which he was performing duties. However, he may be reemployed in other departments. His term of service shall be calculated in accordance with the rules 237 and 238.