machines of this era were called "vented"; their fumes and drying exhausts were sent into the air, in the same way as with modern tumble dryer exhausts. this added to environmental contamination. also much potentially reusable perc was lost to the atmosphere. much stricter controls on solvent emissions have ensured that all dry cleaning machines in the western world are now fully enclosed. no solvent fumes are vented to the atmosphere. in enclosed machines, solvent recovered during the drying process is returned condensed and distilled. so, it can be reused to clean further loads, or safely thrown away. the majority of modern enclosed machines also incorporate a computer-controlled drying sensor, which automatically feels when most traces of perc have been removed from the load during the drying process. this system ensures that only the smallest amount of perc fumes will be released when opening the door at the end of the cycle.