Skip Navigation

Our publications keep professionals working across the public, private, and academic sectors informed on the most important developments and issues in health security and biosecurity.

newspaper on a keyboard


Find an article or report or see all by area, author, or year:

Image of agent fact sheet PDF: Pulmonary or Choking
Agent Fact Sheet
Pulmonary or Choking Agents
Sanjana Ravi

UPMC Center for Health Security, 2014

Date posted:
December 01, 2013

Pulmonary agents (also known as "choking" agents) compose a class of chemical compounds that disrupt normal breathing.


Pulmonary agents (also known as "choking" agents) compose a class of chemical compounds that disrupt normal breathing. They encompass a wide array of gases, including chlorine, ammonia, phosgene, organohalides, and nitrogen oxides.1,2 These compounds have figured prominently in military conflicts; notably, the US Civil War, World War I, the War in Bosnia and Herzegovina, and the Iraq War.3WWI alone saw more than 70,000 cases of gas poisoning among US troops.3 Unlike other chemical weapons, however, the chemicals that function as choking agents play important roles in the civilian and commercial sectors. For example, manufacturers use chlorine and ammonia to refrigerate food, purify water, and synthesize common household products.2,4

Use as a Chemical Warfare Agent

Chlorine: As early as 1863, Confederate soldiers filled artillery shells with chlorine to disarm Union enemies during the US Civil War.3 Chlorine played a similarly significant role during WWI, with German forces employing chlorine gas against their adversaries during the Second Battle of Ypres in 1915.5 Chlorine-based weaponry has also figured into more recent conflicts. During the War in Bosnia and Herzegovina, for example, Bosnian Muslim forces employed 120-millimeter, chlorine-laden mortar rounds against Serbian combatants on at least 3 separate occasions in 1993.6

Phosgene: British physician and chemist John Davy first synthesized phosgene in 1812; it has since become an important component of dye and pesticide production.1,2 During WWI, phosgene emerged as a sophisticated alternative to chlorine gas. Chlorine gas often caused victims to cough and choke violently; phosgene, by contrast, caused much less coughing, resulting in increased gas inhalation.2 Military forces even formulated a "white star" concoction consisting of a phosgene-chlorine mix, and the chlorine vapor in this mix effectively spread the phosgene over a wider geographic area.7 More recently, during the North Yemen Civil War of 1962-1970, Egyptian soldiers employed phosgene-loaded bombs and artillery shells against both Yemeni civilians and Royalist troops.8

Chloropicrin: John Stenhouse, a Scottish chemist, first synthesized chloropicrin in 1848. While it is not as lethal as other choking agents, chloropicrin, which is also known as a riot control agent, induces severe vomiting and excessive tear formation in its victims.9 In 1917, German troops used chloropicrin-filled shells against the Italian soldiers, occasionally adding phosgene to launch especially debilitating assaults.10 Allied forces retaliated by formulating their own cocktail of chloropicrin and stannic acid, which created large clouds of toxic gas over enemy lines.10

Mechanism of Action & Physical Properties

Choking agents function in liquid, gaseous, or aerosolized forms. In their gaseous form, they operate primarily by irritating the respiratory tract-including the mucous membranes, nasal passage, throat, airways, and lungs-and inducing swelling in these areas. Chlorine is a dense, greenish gas at room temperature, and is relatively insoluble in water. Upon inhalation, water inside the body oxidizes chlorine gas to produce hypochlorous acid (HClO). HClO penetrates cells and reacts with proteins to degrade cellular structures. Chloropicrin, meanwhile, is a colorless, highly volatile liquid featuring a sharp odor. A powerful oxidant, it reacts readily with aluminum, magnesium, and their associated alloys to produce a toxic, corrosive gas.11 Phosgene gas, like chloropicrin, is also colorless. Liquid phosgene reacts violently with water and ammonia-decomposing rapidly in both to produce hydrochloric acid and urea, respectively. It also evaporates quickly from the skin, allowing for effective decontamination with water.12,13

Signs & Symptoms

Choking agents enter the body primarily via inhalation, and their effects vary by type and level of exposure. In the short term, low exposure to any of the choking agents typically damages the larger airways. In fact, exposure to as little as 15 parts per million (PPM) of chlorine gas can trigger respiratory irritation, coughing, and chest constriction.3In addition to thoracic and respiratory distress, the immediate effects of choking agent exposure also include burning of the eyes, nose, and throat.14 Chlorine and phosgene gas may also cause blistering and skin lesions, blurred vision, excessive tear formation, nausea, low blood pressure, and heart failure.14 Chloropicrin exposure causes skin irritation, chemical burns, and vomiting, and it inflicts severe damage upon the respiratory lining.15

The long-term results of choking agent exposure include permanent damage to the lung tissues and heart failure.1Although choking agents are intended to be debilitative rather than lethal, very high doses of chlorine, phosgene, or chloropicrin can cause rapid death. Exposure to 1000 PPM of chlorine, for example, is fatal after only a few deep breaths.3

Short- and Long-Term Effects of Choking Agent Exposure

  Thoracic/Respiratory Dermatalogical Cardiovascular Ophthalmological
Short-term Effects

Chest tightness, coughing, wheezing, asphyxiation

Dermatitis, discoloration, blisters, burning sensation, chemical burns

Slow heart rate, low blood pressure

Blurred vision, burning sensation, excessive tear formation

Long-term Effects

Respiratory failure, chronic bronchitis, emphysema


Irregular pulse, congestive heart failure



Immediate diagnosis of lung poisoning is difficult, given the relative nonspecificity of the symptoms associated with choking agent exposure. Furthermore, there is no clinical test for detecting chlorine, chloropicrin, or phosgene in the respiratory system. Diagnosticians must rely instead on patient histories to determine potential routes of exposure.16 Differential diagnosis of choking agent poisoning depends on the presence of mucosal irritation and deep lung effects in addition to the aforementioned symptoms.16


There is no antidote against any of the choking agents. The North Atlantic Treaty Organization (NATO) has undertaken research to devise new therapies for agents of chemical terrorism, but these endeavors have realized only limited success.17 Therefore, medical treatment for those exposed to chlorine, phosgene, or chloropicrin is largely supportive and decontaminative in nature. Specific strategies include secretion management, oxygen therapy, and administration of high-dose steroids to reduce respiratory swelling.16 Intubation and mechanical ventilation maybe required. Caregivers should exercise caution in using sedatives on patients whose airways and breathing are not controlled.


Decontamination is a critical step in mitigating the effects of choking agents. Those who come into physical contact with chlorine, phosgene, or chloropicrin should immediately remove their clothing, making sure to cut contaminated garments off rather than pull them over their faces. Garments should then be sealed in plastic bags for inspection and removal by health authorities. Exposed individuals should also rinse their skin with soap and water, remove their jewelry, and dispose of their contact lenses before seeking medical attention.9,18,19


  1. Pulmonary agents. In Medical Management of Chemical Casualties Handbook. Aberdeen Proving Ground, MD: United States Army Medical Research Institute of Chemical Defense; 1995. Accessed February 26, 2014.

  2. Shea DA. Chemical Weapons: A Summary Report of Characteristics and Effects. Washington, DC: Congressional Research Service 2012. Accessed February 26, 2014.

  3. Pike J. Choking agents. Web site. 2011. Accessed February 26, 2014.

  4. US Department of Health and Human Services. Choking agents. US News and World Report Web site. March 29, 2006. Accessed May 2, 2013.

  5. Duffy M. Battles-the second battle of Ypres, 1915. First World Web site. August 22, 2009. Accessed February 26, 2014.

  6. Bosnia produced chemical arms, report says. New York Times. December 4, 1996. Accessed February 26, 2014.

  7. Duffy M. Weapons of war-poison gas. First World Web site. August 22, 2009. Accessed February 26, 2014.

  8. Egypt overview. NTI Web site. February 2013. Accessed February 26, 2014.

  9. Facts about riot control agents interim document. US Centers for Disease Control and Prevention, Emergency Preparedness and Response Web site. July 30, 2003. Accessed February 26, 2014.

  10. Fries AA, West CJ. Chemical Warfare. 1st ed. New York, NY: McGraw-Hill Book Company, Inc. 1921.

  11. Material safety data sheet-chloropicrin. ASHTA Chemicals, Inc., Web site. February 2012. Accessed February 26, 2014.

  12. Material safety data sheet-phosgene. BOC Gases Web site. June 7, 1996. Accessed February 26, 2014.

  13. Properties of phosgene. American Chemistry Council Web site. 2002. Accessed February 26, 2014.

  14. The facts about chlorine. New York State Department of Health Web site. May 2005. Accessed February 26, 2014.

  15. Miller MG, Laughead G. Chapter III: the lung irritant or "choking" gases. Medical Aspects of Gas Warfare. WWI: the medical front Web site. Accessed February 26, 2014.

  16. Escambia Health. Bioterrorist agents: differential diagnosis, initial laboratory tests, and public health actions. 2001.

  17. Hamilton, MG. Medical countermeasures to Weapons of Mass Destruction: The NATO advantage. In Defence against the Effects of Chemical Hazards: Toxicology, Diagnosis and Medical Countermeasures (pp. KN2-1 - KN2-6). Meeting Proceedings RTO-MP-HFM-149, Keynote 2. Neuilly-sur-Seine, France: RTO. 2007.$MP-HFM-149-KN2.pdf. Accessed February 26, 2014.

  18. Facts about phosgene. US Centers for Disease Control and Prevention, Emergency Preparedness and Response Web site. April 12, 2013. Accessed February 26, 2014.

  19. Facts about chlorine. US Centers for Disease Control and Prevention, Emergency Preparedness and Response Web site. April 10, 2013. Accessed February 26, 2014.

(Last reviewed December 1, 2013)