In my world anyway - municipal utility - a force account is when we receive a construction grant from the state or feds and perform the work with our own forces - not a contractor. This is normally only done for relatively small projects. It typically requires that we provide the granting agency proof that we have the time, manpower, and skill sets to perform the project- along with detailed construction plans and cost estimates. Typically an agent of the grantor will come up and inspect our records and possilbly the construction itself. To get reimbursement we have to submit certified records of all material purchases, equipment hours, and labor. You can usually apply a multiplier to labor costs for benefits, but not always. After project completion you are subject to an audit, but in my experience that usually doesn’t happen.