* No injuries reported due to alky unit release
* Unit was hit by fire in 2009
HOUSTON, March 6 (Reuters) - Citgo Petroleum Corp's 163,000 barrel per day (bpd) Corpus Christi, Texas, refinery shut its hydrofluoric acid alkylation unit after a malfunction late on Monday released chemicals into the air, a local emergency agency and media said.
Water cannons surrounding the alkylation unit went off on detection of a chemical release from the unit, media reported.
No injuries were reported due to the release and air monitors set up around the refinery's East Plant detected no chemicals in the air at locations outside the refinery.
Several streets around the refinery were blocked off after the release, media reported. The Citgo Corpus Christi Refinery East Plant has residential neighborhoods nearby.
Hydrofluoric acid is used in the alkylation unit to make gasoline blendstocks called alkylates that boost octane.
In 2009, an explosion at the Citgo Corpus Christi alkylation unit resulted in a fire that severely injured one worker and came close to scattering hydrofluoric acid over areas around the refinery when the water cannon system nearly failed, according to a federal investigation.
Hydrofluoric acid can severely damage skin, eyes and bones and lead to cardiac arrest in humans.
Hydrofluoric acid alkylation units have been criticized by labor unions and environmental groups for the potential risk the acid poses to plant workers and surrounding communities.
The United Steelworkers union, which represents most U.S. refinery workers, has called for hydrofluoric acid alkylation units to be replaced with those using sulfuric acid, citing the 2009 explosion at the Citgo Corpus Christi refinery.
Citgo is the U.S. refining unit of Venezuela's national oil company PDVSA.