First pause the web shield, that will allow for it to be downloaded, but don't open it as the standard shield would then alert if you extract the files.
Create a folder called Suspect in the C:\ drive, e.g. C:\Suspect. Now exclude that folder in the Standard Shield, Customize, Advanced, Add, type (or copy and paste) C:\Suspect\* That will stop the standard shield scanning any file you put in that folder. You should now be able to export any file in the chest (or other HDD location) to this folder and upload it to VirusTotal without avast alerting.