Gas Poisoning: Symptoms, Types and What to Do

What is gas poisoning?

Gas poisoning is any harm caused by inhaling a toxic gas, vapor or fume. Gases hurt the body in three main ways:

• Chemical asphyxiants stop your blood carrying oxygen or stop your cells using it. Carbon monoxide (CO), hydrogen cyanide and hydrogen sulfide work this way. They mainly affect the brain and heart, which need the most oxygen.
• Simple asphyxiants are not poisonous themselves but push oxygen out of the air in a closed space. Natural gas (methane), propane, nitrogen, carbon dioxide and helium fall into this group.
• Irritant gases burn the eyes, nose, throat and lungs. Chlorine, ammonia, chloramine from mixed cleaners, sulfur dioxide, nitrogen dioxide and phosgene are examples.

Carbon monoxide poisoning causes most deaths from accidental gas poisoning. In the US it sends tens of thousands of people to the ER every year, and cases rise in winter and after power outages, when people run generators and heaters indoors.

Gas poisoning symptoms: signs of toxic gas exposure

Symptoms depend on which gas, how concentrated it is and how long you breathe it. Two patterns cover most cases.

Symptoms of carbon monoxide and other oxygen-blocking gases

CO has no color, smell or taste, so the first sign is often feeling unwell. The symptoms are easily mistaken for flu or food poisoning:

• dull, throbbing headache, the most common symptom
• dizziness and light-headedness
• nausea and vomiting
• weakness and tiredness
• shortness of breath on exertion
• blurred vision
• confusion, poor concentration and clumsiness
• chest pain or palpitations, especially in people with heart disease

Higher levels cause fainting, seizures, an irregular heartbeat, coma and death. The often-quoted "cherry red" skin is rare and usually seen only after death, so normal skin color does not rule CO out.

Clues that point to CO rather than a virus:

• other people or pets in the same place are ill at the same time
• you feel better away from home or work and worse when you return
• symptoms started after turning on the heating, using a gas stove for warmth, or running a generator, grill or car in an enclosed space
• there is no fever

Symptoms of irritant gases

Irritant gases cause burning symptoms from the moment you breathe them:

• stinging, watering burning eyes
• burning nose and throat, and a hoarse voice
• coughing and choking
• chest tightness and wheezing
• shortness of breath
• nausea and vomiting

Gases that dissolve easily in water, such as ammonia and chlorine, hit the eyes and upper airway first, so you notice them quickly and usually escape. Gases that dissolve poorly, such as phosgene and nitrogen dioxide, cause little irritation at first and go deep into the lungs. That is why they are dangerous: you may breathe them for longer without realizing.

Symptoms by type of gas

Is natural gas poisonous?

Natural gas from a leak is mostly methane. Methane itself is not toxic, but a large leak in a closed room lowers the oxygen level, causing headache, dizziness, nausea, tiredness and, in extreme cases, loss of consciousness. The bigger dangers are fire and explosion, and carbon monoxide if gas appliances burn the gas poorly. If you smell the rotten-egg odorant, do not switch lights or appliances on or off, do not use a phone inside, leave the building and call your gas company or 911 from outside.

How soon do gas poisoning symptoms start?

• Carbon monoxide: symptoms can begin within minutes at high levels or build over hours at low levels. Children, pregnant people, older adults and people with heart or lung disease are affected sooner.
• Water-soluble irritants (chlorine, ammonia): within seconds.
• Poorly soluble irritants (phosgene, nitrogen dioxide): a cough and breathlessness can start 2 to 24 hours later, and fluid on the lungs (pulmonary edema) can develop for up to 72 hours.

Can symptoms appear after you leave the fumes?

Yes. Lung injury from irritant gases can worsen over the next day, and anyone with breathing symptoms after a significant exposure is usually watched in the hospital for several hours or overnight. After carbon monoxide poisoning, some people develop delayed neurological sequelae: memory loss, poor concentration, mood or personality changes, movement problems or incontinence, appearing 2 to 40 days after they seemed to recover. Tell a doctor about any new symptoms in the weeks after a CO exposure.

What to do if you suspect gas poisoning

1. Get out. Move everyone, including pets, into fresh air immediately. Do not stay to find the source.
2. Do not create sparks if you smell natural gas or propane. Leave doors open as you go if it is quick and safe.
3. Call 911 or your local emergency number for anyone with symptoms. For advice on a minor exposure, call Poison Control at 1-800-222-1222 (US).
4. Do not go back in until the fire department or gas company says it is safe. Rescuers can be overcome by the same gas, especially in sewers, tanks and silos.
5. Rinse the eyes and skin with plenty of clean water for at least 15 minutes after irritant gas exposure. Remove contaminated clothing.
6. If someone is unresponsive and not breathing normally, start CPR if you are trained and it is safe.

How doctors diagnose gas poisoning

Diagnosis rests on the story of exposure plus tests:

• Carboxyhemoglobin level: a blood test, or a noninvasive pulse CO-oximeter, measures how much hemoglobin is carrying CO. A standard finger pulse oximeter cannot tell CO from oxygen and may read falsely normal.
• Arterial blood gas and lactate: show oxygen levels and whether cells are starved of oxygen, which raises suspicion of cyanide in smoke inhalation.
• ECG and heart enzymes: look for strain on the heart.
• Chest X-ray: looks for lung injury or fluid.
• Pregnancy test: because the fetus is especially vulnerable to CO.
• Neurological examination: checks memory, coordination and alertness as a baseline.

Treatment for gas poisoning

Oxygen

High-flow oxygen through a tight-fitting mask is the main treatment for CO poisoning. It shortens the time CO stays bound to hemoglobin from about 5 hours in room air to around 1 hour.

Hyperbaric oxygen

Breathing oxygen in a pressurized chamber clears CO faster still. It is considered for people who lost consciousness, have confusion or other neurological signs, heart damage, very high CO levels, or who are pregnant, partly to reduce the risk of delayed brain effects.

Treating irritant gas injury

• oxygen and humidified air
• inhaled bronchodilators for wheeze
• steroids in some cases
• breathing support, including a ventilator, if acute respiratory distress syndrome develops

Antidotes

Cyanide poisoning, mostly from house fires, is treated with hydroxocobalamin. Hydrogen sulfide and other specific gases have their own protocols.

Complications and recovery

Most people with mild CO poisoning recover fully once they are treated and the source is fixed. After severe poisoning, long-term problems can include memory and concentration difficulties, depression, anxiety, movement disorders and heart damage. Irritant gases can leave chronic cough, asthma-like symptoms (reactive airways dysfunction syndrome) or scarring of the airways. Smoke exposure carries a risk of chemical pneumonitis and pneumonia.

How to prevent gas poisoning

• Fit CO alarms on every level of your home and outside sleeping areas. Test them monthly and replace them as the manufacturer advises, usually every 5 to 10 years.
• Have furnaces, boilers, water heaters, chimneys and gas appliances checked by a qualified technician every year.
• Never run a generator, grill, camp stove or car in a home, garage, basement or tent, even with a door open. Keep generators at least 20 feet (6 m) from windows and doors.
• Never use a gas oven or stove to heat your home.
• Store and use cleaning chemicals separately, with windows open.
• Never enter a manure pit, sewer, tank or silo without proper training, gas monitoring and a rescue plan.

Frequently asked questions

What are the first signs of gas poisoning?

For carbon monoxide, the first signs are usually a headache, dizziness, nausea and tiredness, often in more than one person at once and improving outside. For irritant gases such as chlorine or ammonia, the first signs are burning eyes, throat irritation and coughing within seconds of exposure.

How do you detect toxic gas in your home?

Carbon monoxide cannot be seen or smelled, so the only reliable detector is a working CO alarm. Natural gas and propane have a rotten-egg odorant added so you can smell a leak. Some utilities and fire departments will test your home if you call. Never rely on symptoms or smell alone.

Can symptoms of gas poisoning start 30 minutes after exposure?

Yes. Carbon monoxide symptoms often build up gradually over 30 minutes to a few hours of exposure. With gases such as phosgene or nitrogen dioxide, breathing problems can begin hours after you leave the area and can worsen for up to 72 hours, which is why doctors may observe you overnight.

Can gas poisoning show up after the fumes are gone?

It can. Lung damage from irritant gases may appear later, and carbon monoxide can cause delayed brain effects, such as memory problems or personality changes, 2 to 40 days after the exposure. Report any new symptoms in the weeks after poisoning to your doctor.

What are the symptoms of natural gas poisoning?

A natural gas leak mainly causes headache, dizziness, nausea, fatigue and shortness of breath because it lowers the oxygen in the air. If gas appliances burn poorly, they also produce carbon monoxide, which causes the same symptoms but more severely. Leave immediately and call from outside.

Does gas poisoning cause a stiff neck or shoulder pain?

A stiff neck is not a typical sign of gas poisoning. CO can cause general muscle aches, weakness and headache. A stiff neck with fever, headache and confusion points more toward meningitis, which is a medical emergency in its own right.

How long does it take to recover from gas poisoning?

Mild carbon monoxide poisoning usually improves within hours of oxygen treatment, though headache and tiredness can last several days. Severe poisoning or significant lung injury can take weeks to months to recover from, and some people have lasting memory or breathing problems.