Journal Highlights Groundbreaking S&T Research on Chlorine Spread

Imagine billowing clouds of deadly, yellow-green gas gushing with force from a tank, undulating, pulsating and spreading in waves over the ground, resembling surging foamy water. Imagine you are a resident in a nearby home—is it safe to remain where you are? Do you need to evacuate? Imagine you are a first responder called to the scene—what protective gear do you need? How can you secure the surrounding area?

That billowing cloud you are picturing is chlorine, the scent of which we all know from our community pools or laundry rooms. Did you know it can kill in minutes if inhaled in high concentration?

Since 2010, the Department of Homeland Security (DHS) Science and Technology Directorate (S&T), the Defense Threat Reduction Agency (DTRA) and other U.S. and international partners from across government, industry and academia have collaborated on Project Jack Rabbit—a groundbreaking field and laboratory research program on toxic inhalation hazards of  industrial chemicals like ammonia and chlorine. As part of this program, S&T led the Jack Rabbit II project, involving multiple large-scale chlorine release experiments at the U.S. Army Dugway Proving Ground in 2015 and 2016. Nine chlorine release trials were successfully performed, and now the research conducted for Jack Rabbit II is in such demand worldwide that it is featured in a special edition of the prestigious peer-reviewed Journal of Atmospheric Environment.

Why do we need such large-scale research on chlorine? Rarely encountered in pure form, chlorine is important as it is used in the production of multiple products we need in our everyday lives, such as cleaning and sanitizing solutions, plastic building materials (polyvinylchloride or PVC), and in some medicines. We also use it in those swimming pools we swim in and in the tap water we drink. Millions of tons of chlorine are produced and transported to industrial plants and factories via road, water and rail across the globe every year. And there lies the danger. En route, while travelling to these facilities, incidents can happen by accident or intentionally by bad actors, threatening civilian lives, especially in densely populated areas.

Recent events highlight the need for responders to be prepared with the best information possible for this type of hazard. For instance, in June 2020, dozens of people were treated for chlorine exposure during an incident at a hazardous material storage facility at a U.S. military base in Okinawa, Japan. Another 25 were hospitalized in June after a chlorine gas leak at waterworks in Mohali, India. In July 2020, 70 people were injured by chlorine inhalation after a fire at a power plant in Iran.

“Large scale releases of chlorine have never been tested and studied at the volumes representative of shipments via tanker truck (20 tons) or railcars (90 tons),” said Dr. Shannon Fox, Jack Rabbit II principle investigator and director of S&T’s Chemical Security Analysis Center (CSAC). “Outdoor field testing affords the unique opportunity to study this type of release scenario and directly address critical data and knowledge gaps to improve hazard prediction modeling, emergency response, and industrial safety and security.”

“We do a substantial environmental assessment before the large-scale outdoor release and coordinate with the test site state authority, so no one is injured, and environmental impacts are minimized,” added Dr. Sun McMasters, CSAC physical chemist and current Jack Rabbit program manager.

Special journal issue highlights an extraordinary collaborative accomplishment

The special issue of the Journal of Atmospheric Environment will contain a cluster of 18 articles, with two co-authored by CSAC involving the Jack Rabbit II field and lab tests. Subject matter experts submitted an additional 16 manuscripts presenting summary test results used for model inter-comparisons, results from comparisons of different dispersion models, as well as some results of related research on flow fields around obstructions and chemical reactions with surface materials.

The first CSAC-authored article in the special issue presents an introduction and overview of the Jack Rabbit II field experiments involving releases of 5-20 tons of liquefied chlorine. The article describes the chlorine releases for which the researchers arranged a combination of over 80 shipping containers at the test site to represent an urban area with one- and two-story buildings, capturing the releases with LIDAR (similar to radar but uses laser light instead of radio waves), video and still cameras.

The second article co-authored by CSAC focuses on lab experiments conducted at the University of Arkansas to measure the degree to which plants and soil absorb chlorine to help decrease the spread of the gas. During a release, chlorine reacts with plants, destroying their tissue.

“If you have more vegetation, more soil, more environmental material that absorbs the chlorine, this means there is likely less downwind hazard,” said McMasters. “The purpose of this study was to investigate potential mitigation strategies using environmental materials and learn how much of chlorine can be removed. This will also help modeling better predict the actual spread of chlorine.”

The remaining articles were authored by researchers from the US, UK, Sweden, France, Finland, China and the European Commission. The feature inter-comparison article compares 17 widely-used dense-gas prediction modeling tools using the Jack Rabbit II field trial data (mass release rate, wind speed, wind direction and detection concentrations) with the goal of analyzing hazardous gas releases and identifying gaps to be addressed in future analysis and studies. This will help improve harmonization of the models and provide guidelines to response in the event of a chlorine release.

“The special issue of Atmospheric Environment is an extraordinary collaborative accomplishment that highlights the far-reaching impact of Jack Rabbit II,” said Fox. “This demonstrates and validates a highly successful model of S&T leading a groundbreaking multifaceted program, securing extensive interagency partnerships, and mutually sharing data and resources to greatly enhance the program’s impact and return on investment.”

Jack Rabbit’s impacts and future efforts

The Jack Rabbit research has greatly improved and will continue to improve hazard prediction modeling, emergency planning and response strategies against chemical release incidents. CSAC used Jack Rabbit II findings to update modeling for Pamphlet 74, a product furnished by the Chlorine Institute to help chlorine producers, local emergency planning committees, fire departments and municipalities estimate areas affected by potential chlorine release incidents. Also, the project findings informed the U.S. Department of Transportation’s work related to large-scale chlorine releases, guided improvements to DTRA’s atmospheric transport and dispersion and hazard prediction models, and informed DHS agencies how to train first responders for large chlorine incidents. 

Next year, CSAC researchers will embark on a new round of Jack Rabbit research—Jack Rabbit III—which will focus on developing strategic technology solutions for chemical incident countermeasures, decontamination, protection, emergency response, training and national level exercises. Planned experiments include laboratory, wind tunnel and chamber testing, and large-scale open-field tests with Anhydrous Ammonia, the foundation of nitrogen fertilizers.  

“Jack Rabbit III will expand on previous work and build security, safety and resilience in the chemical supply chain through experimentation over the next five years,” said Fox. “Jack Rabbit III is building on the success of the Jack Rabbit II trials and significant impacts made in securing the homeland from persisting chemical threats.”

For more information, please contact CSAC at [email protected]. For related media inquiries, please contact [email protected].