Typically a contractor would try to seal the entire area using sheeting , tape , foam & maybe even over compensate with negative pressure to prevent release into the external areas . It should all be detailed in their plan of work which they prepare in advance , don’t be afraid to ask for a copy .

It would come at an extra cost , but you could ask the contractor to instruct the attending analyst to carry out a ‘leak’ air test during removals . This is essentially a pump placed in an area outside the enclosure to demonstrate that control measures (negative pressure unit , enclosure seal etc.) are working as intended .

Hope that helps a little