Pork roast safe cooking
As seen in simplest form here, the FDA has deemed the temperature danger zone at between 41°F and 135°F inclusive.

Meanwhile, also in its simplest form here, we see again from the FDA that the internal temperature of pork must come to 145°F in order to be considered safe.

Finally, consider the following, as found here


  Crock pots may vary but generally, the LOW setting is about 200
  degrees F. and the HIGH setting is about 300 degrees F.


These three pieces of information in combined form make it certain that you're in no danger of having spoiled your cut of meat by cooking it only on Low for 30 minutes.