Q20. Can we use the crosswind air barrier in our hair salon against infection?

Yes, certainly.  This is one the best close-encounter settings where mitigation performance will be at maximum from the crosswind air barrier.  That is because both the hair stylist and your customer are not moving relative to the air stream and the air barrier can be maintained in one direction.  In this setting it is best to aim the air stream so it blows from the top down [view here in Part 1], and your customer can safely remove her mask as long as your stylist is not directly in front of her.