Once the building is sealed off, the exterminator must weigh the facts and determine what chemical is best to kill off the pest or pests that are making life miserable. The team must determine how much of the gas is necessary to kill off the colony of pests, because there is no benefit in just spewing out chemicals without restraint.
There is such a thing as automatic fumigating equipment, so the exterminator doesn’t have to stay inside the building while the process is underway. However, he/she will enter the building and wear a heavy biohazard protection suit for safety. The purpose of entering will be to monitor gas levels with special equipment and ensure the right concentration is being used. The exterminator may also monitor how the treatment is working. (Dead Bodies Everywhere by Korn, anyone?) Homeowners and business owners should not enter until the readings indicate it is safe to go inside.