Scenario A: Marty, of the local public swimming pool, is preparing for the upcoming season. He enters the maintenance shed, where 55 gallon drums of liquid chlorine are being stored.

Scenario B: Tabitha did not use her backyard pool last year, as she did not want to deal with the headache of maintaining the water quality throughout the season. This year, she has decided to give the pool another shot, and enters the locked pool shed to retrieve a tub of pool chlorination granules that she recalls leaving there two years ago.

Scenario C: Bartholomew is a very clean person. Today, he decided to increase his germ-fighting power by mixing bleach and ammonia together in a bucket. For good measure, he also decides to add a little bit of white vinegar to the mix to help dissolve the mineral scale in his bathroom.

Scenario D: Firefighter Donald responds to a working fire at a home that has been decoratively layered with PVC siding. Because he was operating on the exterior of the building, he neglected to use his respiratory protection. As the winds pick up, he begins to inhale a significant quantity of smoke.

The common denominator of all of these scenarios is the potential for exposure to chlorine gas or chlorinated compounds, such as chloramines or hydrogen chloride. These scenarios are not particularly far fetched… though chlorine exposure has been related to industrial accents and terrorist attacks, the more likely prehospital encounters will include these individual and occupational exposures.

What is chlorine, and where does it come from?

Chlorine is a chemical element.

…and it’s everywhere. It’s the 21st most abundant element in the Earth’s crust, and is most commonly found in table salt (sodium chloride). This is no coincidence, as chlorine has the highest electron affinity of any of the elements, meaning that it really likes to react with other elements to form more stable molecules. At normal temperatures and pressures, the element exists as a diatomic gas (Cl2) that is very weakly held together. Chlorine gas in this form is usually encountered in industrial and scientific circles, as the majority of individual and occupational exposures tend to involve inadvertent production of the gas through chemical reactions, or exposure to a chlorinated agent. 

Its commercial production is usually achieved through electrolysis (application of strong currents) of a salt solution. For the chemically-inclined, the reaction is fairly straight forward:

2 NaCl + 2 H₂O → electricity → Cl₂ + H₂ + 2 NaOH  

Table Salt + Water → electricity → Chlorine Gas + Hydrogen Gas + Sodium Hydroxide

Some of the hydrogen gas can be further combined with the chlorine gas to commercially produce hydrochloric acid (HCl).

Incidentally, chlorine gas (also known as ‘bertholite’) was the first gaseous chemical warfare agent to be used, making its debut in World War I in 1915. Since then, chlorine bombs have been used in other conflicts, including the Iraq War and the conflict between the Islamic State and the Kurdish.

In recent history, many of the major domestic chlorine-related incidents involved rail transport of large quantities of the gas. In 2005, a railroad tanker traveling through Graniteville, SC was erroneously routed onto a track that led to a collision with another train with subsequent release of 90 tons of chlorine gas. In 2007, a technician error occurred while transferring chlorine from a rail car to storage containers at a bleach factory in Tacoma, WA. This resulted in the release of over 900 pounds of chlorine gas, and the hospitalization of twelve first responders, who were overcome when the wind shifted.

With a basic understanding of what chlorine is and how it is commercially produced, we can now turn our attention to the sorts of reactions that are likely to lead to individual exposures. If the chemistry of chlorine gas generation doesn’t appeal to you, go ahead and skip down to the medical stuff.

Three reactions, in particular, apply to all the above scenarios (for the chemistry nerds among you — I intended to keep the equations unbalanced so that they would be simpler-looking):

Reaction 1 (Bleach in Water):

NaOCl   +   H20   →   HOCl   +   NaOH

Bleach + Water → Hypochlorous Acid + Sodium Hydroxide

Reaction 2 (Equilibrium of Bleach with Chlorine Gas):

HOCl   ⇌   H+   +   OCl−   +   Cl−   ⇌   Cl2   +   H2O

Hypochlorous Acid ⇌ Acid + Hypochlorite + Chloride  ⇌ Chlorine Gas + Water

⇌ indicates that the reaction can go either way depending on the conditions (ie. pH)

Reaction 3 (Formation of Chloramines by Mixing Bleach and Ammonia):

NaOCl   +   NH3   →   NH2Cl   +   NHCl2   +   NaOH

Bleach   +   Ammonia   →   Monochloramine   +   Dichloramine   +   Sodium Hydroxide

 Scenario A: Liquid Chlorine

Liquid chlorine is chemically identical to bleach (NaOCl; Sodium Hypochlorite), but is stronger. Usually it has 10-15% available chlorine (compared to 5.25% in Clorox, which is commonly diluted to 1-2% before use, and 0.5%, which is needed to inactivate C. difficile spores), and because its production involves bubbling the chlorine through a solution of caustic soda, it is a very strong base (pH ~13). When the chemical contacts water, it undergoes a rapid reaction to form hypochlorous acid (see Reaction 1 above). The hypochlorous acid is actually the agent that is responsible for the disinfectant properties of chlorine. As hypochlorous acid exists in equilibrium with chlorine gas (see Reaction 2 above), the chlorine can bubble out of solution when left exposed to the air. In a confined space, such as the maintenance shed described above, accumulation of this gas over a prolonged period can result in significant accumulation of these toxic fumes.

Scenario B: Chlorine Tablets

Chlorine tablets and granules come in a variety of forms. Trichloro-s-triazinetrione (“Tri-chlor”) is a stabilized form of chlorine, yielding ~90% available chlorine. Dichloro-s-triazinetrione (“Di-chlor”) is another form of stabilized chlorine, with ~62% available chlorine. Lithium hypochlorite has approximately 35% available chlorine, and calcium hypochlorite has approximately 65% available chlorine. Of the entire gamut, the most dangerous and unstable is the calcium hypochlorite. As it is very dusty and easily contaminated, it is prone to explosive reactions when in contact with other foreign chemicals. All of the above can be subject to spontaneous decomposition over time, yielding production of chlorine gas (see Reaction 2 above). Concentrated chlorine gas can also be generated when the tablets are added to the water in the presence of swimmers.

Scenario C: Bleach and Acid / Ammonia

This is the leading cause of most nonoccupational exposures. When bleach is dissolved in water, there are several chlorine components that exist in equilibrium. The acidity (pH) of the solution is what determines which component is most prevalent. When the pH is more basic (>7.4), the predominant ion is hypochlorite. When the pH is between 2 and 7, the equilibrium favors hypochlorous acid. For this reason, maximum disinfecting efficacy is achieved at pH 4-5. At a very low (acidic) pH, the reaction favors the production of chlorine gas. Thus, in this case, the addition of vinegar to the bleach would increase the off-gassing of chlorine (and this would be true for any other acidic chemical added to the bleach).

In addition to the direct formation of chlorine gas, the combination of bleach and ammonia (see Reaction 3 above), results in the formation of chloramines (chlorinated nitrogenous compounds). These chloramines can be toxic, just like chlorine.

Scenario D: Burning of PVC and Plastics

Many plastics, especially PVC (polyvinyl chloride) will produce chlorinated compounds when they are burned. One of the more dangerous of these gases is hydrogen chloride (HCl). You’ll note that hydrogen chloride has the same chemical formula as hydrochloric acid (HCl). In order for the gas to become hydrochloric acid, it must dissolve into water (such as the water in your lungs). As homes continue to contain more synthetic materials in their construction and contents, there exists significant potential for the production of hydrogen chloride by pyrolysis. The same principal applies to the burning of plastics in campfires and fireplaces.

The health effects of chlorine gas, chloramines, and hydrogen chloride:

Chlorine Gas

This is an NFPA 704 diamond (“Hazard Diamond”). It provides a quickly recognized and understood system to give a sense of the hazards of a material and their severities. The three hazards are health (blue), flammability (red), and reactivity (yellow). The white area indicates special hazards (in this case, OX indicates that the substance is an oxidizer). Each part of the diamond is ranked from 0-4, and 4 represents the greatest hazard.

Chlorine’s toxic effects are primarily due to the production of hypochlorous and hydrochloric acid that occurs when the gas reacts with water (such as that in the lungs or mucous membranes). Likewise, the inhalation of hydrogen chloride results in the production of hydrochloric acid. These acids can continue to cause damage through the production of free oxygen radicals, which potentiate cellular damage. Commonly, exposure will result in local irritation of the respiratory tract, resulting in bronchospasm, cough, and dyspnea. If cellular damage is significant enough, pulmonary edema and Acute Respiratory Distress Syndrome (ARDS) can result. These are likely to constitute the most severe presentations of exposure, and may necessitate airway and ventilatory support. Beyond the respiratory system, dermal and ocular complications such as chemical burns and conjunctivitis can occur.

Important to note, the solubility properties of chlorine gas may allow individuals to tolerate more prolonged exposures. Irritant gases with a high water solubility (such as ammonia) will rapidly irritate the mucosa, allowing an individual to escape an area of exposure. Gases with very low water solubility (such as phosgene) result in an absence of warning properties, permitting longer exposures. As chlorine gas has an intermediate solubility, it has some warning properties, but may allow for prolonged exposures.

Chloramines

Like chlorine gas, when chloramines dissolve into the fluid of the respiratory epithelium, hypochlorous acid, ammonia, and oxygen radicals are all generated, which act as irritants. Like chlorine gas, the chloramines are less water soluble than ammonia, but they do result in prompt development of mild symptoms. Because these initial symptoms may be mild, individuals may not immediately escape the environment. As exposure becomes cumulative, the presentation may become more severe.

Initial Response and Treatment:

As with all hazardous materials exposures, only highly trained HazMat teams should attempt entry into the Hot Zone. Patient treatment should never be rendered near the site of exposure. Chlorine gas is unlikely to produce a tangible contaminant on clothing, but exposure to liquid chlorine or other agents may. Appropriate decontamination should always include doffing of all patient clothing (the single most effective decontamination strategy), followed by copious irrigation with water (3-5 minutes of rinse time has been advocated). Contact lenses should be removed from patients for irrigation. Attempts at neutralization with a base should not be attempted, as further chemical injury or thermal injury may result through the exothermic reaction of the two chemicals. While chlorine gas becomes acidic in the presence of water, this effect would be mitigated by the large volumes of water used for irrigation, which would simultaneously dilute the acid and dissipate thermal energy.

First responder safety is, of course, paramount. In addition to noting the potential for environmental change (ie. wind), responders should know that chlorine gas is heavier than air, and will naturally sink into lower areas. Consequently, higher ground affords protection from pockets of chlorine gas.

Patient management is largely supportive. Airway patency and ventilatory adequacy must be assured. Bronchodilators may be used for bronchospasm. If a patient must be intubated, low tidal volumes should be used, consistent with current recommendations for ventilation of ARDS; minute ventilation can be maintained by increasing respiratory rate. As patients with minimal initial symptoms can develop delayed pulmonary edema over the course of several hours, transport should be recommended so that observation can occur for 8 to 24 hours in a controlled hospital setting.

Neutralization Therapy

Because the lungs have a large surface area relative to the amount of contaminant present, the heat and gas generated during neutralization can be dissipated (contrary to an ingestion). Case studies suggest that nebulized 2% sodium bicarbonate may be beneficial in patients poisoned by acid-forming irritant gases (most frequently chlorine gas). This benefit does not appear to extend to patients exposed to chloramine, though administering nebulized bicarbonate appears to be safe. In one non-randomized, placebo-controlled, prospective study of patients who were poisoned with chloramine and chlorine, nebulized bicarbonate failed to show any clinically significant improvement over standard treatment. To avoid irritation, the sodium bicarbonate solution must be sufficiently diluted. Usually 1 mL of 7.5%  sodium bicarbonate (“crash cart bicarb”) is added to 3 mL sterile water (~2% final solution concentration). Care must be taken not to mix the bicarbonate with albuterol, as this can form precipitates. Ultimately, it is unclear whether nebulized bicarbonate therapy changes the course of irritant-induced pulmonary damage.

Corticosteroids

Clinical data on the efficacy of corticosteroids used in human beings exposed to pulmonary irritants is limited and inconclusive. There is some suggestion of an early benefit, though methylprednisolone has been associated with increased mortality at 60 and 180 days (when steroids were continued beyond the first 14 days). Most animal studies, do not appear to suggest a benefit, especially after severe exposure, though one animal model showed a benefit of inhaled budesonide if administered within 30 minutes of exposure. As most studies of corticosteroids in ARDS involve septic or traumatized patients, external validity of these data towards pulmonary irritants is limited. Currently, there is little reason to assume a benefit of corticosteroids in the treatment of these patients. However, because most studies demonstrate a tendency towards improvement (with little identifiable risk) the use of steroids appears to remain routine.

Summary of Prehospital Approach to Chlorine:

1. The most frequently encountered chlorine exposures will be individual, and commonly involve inappropriate combination of cleaning ingredients or mishaps with pool supplies.
2. Acidification of bleach yields chlorine gas.
3. Combination of bleach with ammonia yields chloramines.
4. Burning of synthetic materials, especially PVC, can result in formation of hydrogen chloride gas.
5. The first consideration in response should be responder safety. Entry into the Hot Zone should be limited to specialized HazMat personnel. Sufficient perimeters should be maintained to account for changes in environmental conditions, such as wind. Respiratory protection should be worn while operating in the area of exposure.
6. Chlorine is heavier than air, and will sink into depressions in the ground.
7. Decontamination should ubiquitously include doffing of exterior clothing. This may be sufficient for exposure to gaseous chlorine. Exposure to liquid chlorine will necessitate copious irrigation for at least 3-5 minutes with water.
8. Treatment is supportive. Pay special attention to maintaining airway and supporting breathing.
9. Evidence to support a clear benefit of parenteral or inhaled corticosteroids is lacking. The same is true of nebulized bicarbonate. Small studies and anecdotal evidence demonstrating possible benefit with low risk have permitted their use to continue.
10. Patients with minimal symptoms should still be encouraged to seek hospital observation, as pulmonary edema may develop after several hours.