Abstract: An HF alkylation unit with improved safety features including an acid storage and evacuation receiver which maintains a large proportion of the acid inventory of the unit at a remote, safe location. The unit also has an acid evacuation system which is capable of transferring the acid from the reactor section of the unit to the receiver within a very short period of time in the event of an uncontrolled release from the unit. The acid receiving drum is connected to the remainder of the unit by means of acid transfer lines for rapidly evacuating the acid and is desirably maintained at a pressure lower than the reactor section of the unit to enable the acid to be pressured into the receiver. The pressure in the receiver is suitably maintained by a pressure balancing line to the fractionation system at a lower pressure than the alkylation reaction itself. Unit acid inventory may be reduced by the use of an acid settler provided with an acid boot and coalescing baffles which promote a phase separation.