The Transportation Security Administration (TSA) sent out a Security Awareness Message to industry partners (including tank truck fleets) to encourage them to be aware of the potential threat posed by homegrown violent extremists (HVE).
Recent reporting in open source media has referred to the use of an improvised device designed to disperse hydrogen sulfide gas in enclosed spaces, possibly including transportation vehicles or venues.
Hydrogen sulfide is a toxic inhalation hazard (TIH) material, and if a sufficient quantity were to be released in a confined space such as a conveyance, it could reach potentially dangerous concentrations. Hydrogen sulfide has poor warning properties, meaning that a person’s ability to detect its characteristic rotten-egg odor degrades rapidly with exposure to it.
Additional information about hydrogen sulfide can be found at https://www.osha.gov/Publications/hydrogen_sulfide.html .
At this time, the TSA Office of Intelligence and Analysis (TSA OIA) is not aware of any current or credible plots to attack transportation within the United States. However, TSA OIA remains concerned with terrorist organizations’ efforts to conduct attacks against transportation. Threat actors in the Homeland may be influenced by successful overseas attacks to target transportation in the United States.
The current National Terrorism Advisory System (NTAS) Bulletin issued on May 15, 2017 regarding the threat from HVEs remains in effect (http://www.dhs.gov/advisories).
(U//FOUO) These media reports serve as a reminder that transportation systems that carry passengers remain a potential target for terrorist activity. TSA encourages operators to remind employees and passengers to be aware of their surroundings and to report suspicious activities in accordance with company procedures. Persons whose behavior does not fit their circumstances or surroundings should be brought to the attention of law enforcement: “If you See Something, Say Something.” Similarly, unattended items that appear suspicious should also be reported. Examples could include containers of unidentified liquids.