Phosgene Exposure

What is phosgene?

Phosgene is a colorless gas at room temperature. In low concentrations it smells like newly mown hay or green corn; at high levels it is sharp and suffocating. Many people cannot smell it at harmful levels, and the nose quickly gets used to it, so smell is not a reliable warning. It is heavier than air and collects in low-lying areas and basements.

Where exposure happens

• Chemical manufacturing: phosgene is widely used to make polycarbonate plastics, polyurethanes, dyes and pesticides. Leaks and accidents are the main source of serious exposures.
• Heated chlorinated solvents: methylene chloride, chloroform, carbon tetrachloride and some degreasers can form phosgene when exposed to flames, hot surfaces or welding arcs.
• Fires involving chlorinated plastics such as PVC. See smoke inhalation.
• Warfare and terrorism: phosgene caused most chemical-weapon deaths in World War I and is classed as a choking (pulmonary) agent.

How phosgene damages the lungs

Phosgene does not dissolve easily in the moisture of the nose and throat, so it travels deep into the tiny air sacs (alveoli). There it reacts with the cell lining and the thin barrier between the air sacs and blood vessels. Over hours, fluid leaks into the air spaces, causing noncardiogenic pulmonary edema, which can progress to acute respiratory distress syndrome (ARDS).

The higher the dose (concentration multiplied by time), the shorter the symptom-free period and the worse the lung injury. Physical exertion after exposure makes edema worse.

Symptoms of phosgene exposure

Early (minutes)

• Eye burning, watering and redness
• Sore, burning nose and throat
• Coughing, choking sensation
• Chest tightness
• Nausea, sometimes vomiting
• Skin irritation, or frostbite-like burns from contact with liquid phosgene

These can be mild or absent at lower doses.

Delayed (usually 2 to 24 hours)

• Worsening shortness of breath
• Rapid, shallow breathing
• Cough with frothy white or pink-tinged sputum
• Low oxygen levels, blue lips (cyanosis)
• Low blood pressure and shock in severe cases

Symptoms appearing within about 4 hours suggest a large exposure and a worse outlook.

Phosgene vs other irritant gases

The mild early symptoms are why phosgene is so dangerous: people may not leave the area quickly or seek care. Compare chlorine gas exposure and ammonia exposure.

What to do after exposure

1. Leave the area and get to fresh air, moving upwind and to higher ground. Do not re-enter to rescue others without protective equipment.
2. Call 911 or your local emergency number. Tell them phosgene or chlorinated solvents may be involved.
3. Remove clothing that may hold gas or liquid, cutting it off rather than pulling it over the head, and seal it in a plastic bag.
4. Rinse skin with plenty of water and soap. Rinse eyes with water for 10 to 15 minutes, removing contact lenses.
5. Rest completely. Sit up if short of breath. Avoid walking or any exertion.
6. Do not wait for symptoms. Even without symptoms, you need medical assessment.

Hospital assessment and treatment

There is no antidote for phosgene. Treatment is supportive:

• Observation: people with significant or uncertain exposure are typically monitored for at least several hours and often up to 24 hours or longer, because lung edema can be delayed. Those who stay well, with normal oxygen levels and chest X-rays, are usually discharged afterward with clear return advice.
• Strict rest to limit edema
• Oxygen, and breathing support with CPAP or a ventilator using positive pressure if edema develops
• Bronchodilator inhalers for wheezing
• Chest X-rays and blood oxygen tests, repeated over time
• Careful fluid management and treatment of low blood pressure
• Antibiotics only if a bacterial lung infection develops later

Steroids and other drugs have been tried, but none has been proven to prevent lung injury in people.

Outlook and long-term effects

People who survive the first 48 hours usually recover, often within days to weeks. Some have longer-term problems:

• Shortness of breath on exertion and reduced lung function
• Asthma-like symptoms (reactive airways dysfunction syndrome)
• Chronic cough, or bronchitis in heavy exposures

Follow-up lung function tests help track recovery.

Prevention

• Never use chlorinated solvents near open flames, heaters or welding; ventilate well
• Follow workplace safety rules: gas detectors, respirators, training and emergency plans in facilities that use phosgene
• Know your site's evacuation procedures and shelter-in-place instructions during chemical incidents

Frequently asked questions

What does phosgene smell like?

At low concentrations phosgene smells like freshly cut hay, grass or green corn. At high concentrations it has a sharp, choking odor. Many people cannot detect it at harmful levels, and the sense of smell fades quickly with exposure, so smell is not a safe warning sign.

How long after phosgene exposure do symptoms start?

Eye and throat irritation can start within minutes, but the dangerous lung symptoms usually appear 2 to 24 hours later, sometimes after a period of feeling well. The sooner breathing symptoms appear, the larger the exposure likely was. This delay is why observation in hospital is important.

Is there an antidote for phosgene?

No. Treatment focuses on removing the person from exposure, decontamination, rest, oxygen and breathing support while the lungs heal. Early hospital monitoring allows breathing support to start quickly if fluid builds up in the lungs.

Can heating paint stripper or degreaser make phosgene?

Yes. Chlorinated solvents such as methylene chloride, chloroform and carbon tetrachloride can break down into phosgene when they contact flames, hot metal or welding arcs. Use these products only with good ventilation and keep them away from heat sources.