According to a statement from Shell, low levels of benzene were detected at the facility, prompting the cautionary order at the site near Highway 225 and Beltway 8.
The company didn't immediately say any injuries were reported.
Shell's statement said the company uses standards more stringent than OSHA in terms of "permissible exposure limits."
"In this case, the chemical readings we are seeing are at or below the OSHA permissible exposure limits but above Shell HSSE standards requiring a shelter in place," the statement said.
It continued, "Individuals in the community seeking more information on air quality should contact their local office of emergency management."
The safety order comes in the shadows of a separate chemical fire at the Intercontinental Terminals Co. site, which is five miles away from the Shell complex. Up to eight tanks burned during the ordeal that took place over the course of three days.