Carbon Dioxide

Classification

Gas under pressure (liquefied gas); Simple asphyxiant

Hazard statements

• H280 Contains gas under pressure; may explode if heated.
• May displace oxygen and cause rapid suffocation (asphyxiant hazard; no H code).

Key precautionary statements

• P271 Use only outdoors or in a well-ventilated area.
• P282 Wear cold-insulating gloves and face shield or eye protection when handling liquid or solid forms.
• P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
• P410+P403 Protect from sunlight. Store in a well-ventilated place.

The federal OSHA PEL is 5000 ppm (9000 mg/m³) as an 8-hour TWA, from Table Z-1. NIOSH recommends 5000 ppm as a 10-hour TWA and a 30,000 ppm STEL. ACGIH uses the same pair of values, and Cal/OSHA also adds the 30,000 ppm STEL. The IDLH is 40,000 ppm (4%). Carbon dioxide is a normal part of outdoor air at a few hundred ppm, so the hazard comes from leaks, dry ice and fermentation or combustion in poorly ventilated areas. Because it has no odor, use continuous gas detection where it is stored or used in bulk. State OSHA plans may set different limits.

• Appearance: Colorless gas; shipped as a liquefied compressed gas or refrigerated liquid, and sold as a solid (dry ice)
• Odor: Odorless
• Molecular weight: 44.0
• Boiling point: Sublimes (turns straight from solid to gas) at -109°F (-78°C)
• Flash point: Not applicable (nonflammable gas)
• Explosive limits: Not applicable
• Vapor pressure: 56.5 atm
• Relative gas density: 1.53 (heavier than air; collects in low spots)
• Water solubility: 0.2% at 77°F; forms weak carbonic acid

Inhalation

Rising levels cause faster breathing, headache, dizziness, restlessness, tingling, sweating, a racing heart and raised blood pressure. Very high levels cause confusion, convulsions, unconsciousness and death within minutes. Carbon dioxide is more than a simple asphyxiant: it affects the body directly even when oxygen is still near normal.

Skin

The gas does not harm skin. Contact with dry ice, liquid or very cold gas causes frostbite.

Eyes

Contact with liquid, dry ice or cold gas can freeze eye tissue.

Ingestion

Not a relevant route for the gas. Swallowing dry ice can cause severe cold injury.

Target organs

Respiratory system, cardiovascular system, central nervous system

Long-term effects

No long-term effects are expected at levels below the exposure limits. Severe oxygen deprivation during an acute event can leave lasting brain or heart damage.

Gloves

Loose-fitting, cold-insulating gloves when handling dry ice, liquid CO₂ or cold equipment. Work gloves for moving cylinders.

Eyes and face

Safety glasses with side shields for cylinder work; add a face shield where liquid or dry ice could splash or spray.

Respiratory

Air-purifying respirators do not protect against carbon dioxide or low oxygen. NIOSH lists supplied-air respirators or a full-facepiece SCBA up to 40,000 ppm, and a pressure-demand SCBA for emergencies, unknown concentrations or confined space rescue.

Clothing

Long sleeves and insulated clothing when handling cryogenic liquid or large amounts of dry ice.

Store cylinders upright and secured, with valve caps on, in a cool, dry, well-ventilated area away from sunlight and heat. Keep cylinder temperature below 125°F (52°C). Move cylinders on a hand truck rather than rolling or dragging them.

Never store dry ice in a sealed container, walk-in cooler or small unventilated room, because the gas it gives off can build up to dangerous levels and burst tight containers. Install CO₂ monitors where bulk tanks (such as beverage systems) or dry ice are kept indoors, and check the air before entering pits, tanks and cellars. Good ventilation at floor level matters because the gas sinks.

Keep away from

• Reactive metal dusts such as magnesium, aluminum, titanium and zirconium, which can ignite in carbon dioxide
• Strong bases

• Evacuate the area, especially basements, pits and other low spots where the gas collects.
• Do not enter without SCBA until air monitoring shows safe CO₂ and oxygen levels.
• Stop the leak if it can be done safely, and ventilate the area.
• Let spilled dry ice or liquid evaporate in a well-ventilated area; avoid skin contact.
• Follow ERG Guide 120.

Suitable extinguishing media

• Carbon dioxide does not burn; it is itself a firefighting agent
• Water spray to cool containers
• Media suited to the surrounding fire

Special hazards

Cylinders and tanks may burst when heated. Discharges, including from fixed CO₂ fire suppression systems, can quickly make a room unsurvivable, so evacuate before discharge and use SCBA to re-enter. Hot magnesium and some other reactive metals keep burning in carbon dioxide.

• OSHA Hazard Communication (29 CFR 1910.1200): Hazardous chemical (gas under pressure, simple asphyxiant). Labels and safety data sheets are required.
• OSHA Air Contaminants (29 CFR 1910.1000, Table Z-1): PEL 5000 ppm (9000 mg/m³) TWA.
• OSHA Permit-Required Confined Spaces (29 CFR 1910.146): Atmospheres with toxic gas or low oxygen must be tested before entry.
• EPA: Not listed as a CERCLA hazardous substance (40 CFR 302.4), an EPCRA extremely hazardous substance (40 CFR 355), a TRI chemical, or a Clean Air Act 112(r) regulated substance (40 CFR 68.130).
• DOT (49 CFR 172.101): UN1013 Carbon dioxide, Division 2.2; UN2187 Carbon dioxide, refrigerated liquid, Division 2.2; UN1845 Dry ice, Class 9.

• NIOSH Pocket Guide: Carbon dioxide
• OSHA Occupational Chemical Database: Carbon Dioxide
• NOAA CAMEO Chemicals: Carbon Dioxide
• Sigma-Aldrich SDS: Carbon dioxide
• CCOHS Chemical Profile: Carbon Dioxide