Think of what reactions can go wrong (i.e., worst case scenario) and their relative exothermic potential; then think if there would be any difference in the way a standard fume hood would contain the reaction and the way a ductless hood would handle the same event.  Since you are using flammables and acids in the same hood, although not necessarily at the same time, think of what would happen if the two were inadvertently put together because  an undergraduate may have mislabeled a beaker.  

From: "Richard W. Denton" <rwdenton3**At_Symbol_Here**GMAIL.COM>
To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU
Sent: Tuesday, March 18, 2014 3:59:07 PM
Subject: [DCHAS-L] Ductless fumehoods or Not.
Hi everyone:
   I was asked by my department to assist in deciding whether to purchase ductless fumehoods  for our undergraduate chemistry labs. We are planning to use these for flammable solvents, and reactions involving  HCl and NaOH.  These hoods will be used by undergraduates for research also.  Any input on the safety issues involved with these equipments versus the regular hoods would be appreciated.
-Richard (CHO)