Others have covered the basics of your query but here are some additional details. The BWI Guest laundry is near the 3rd floor elevators and are available 24 hrs per day. As
@Best Aunt indicated the laundry view web site offers real time status of the machines.
Also the machines take Debit and Credit cards. They have a vending machine with HE Soap, Rinse and Dryer sheets but you might want to throw your own products in your luggage if you have sensitivity issues. Soap pods and a few dryer sheets don't take up much room.
Dave