Nitrogen Dioxide

Classification

Oxidizing gas, Category 1; Gas under pressure (liquefied gas); Acute toxicity (inhalation), Category 1; Skin corrosion, Category 1; Serious eye damage, Category 1

Hazard statements

• H270 May cause or intensify fire; oxidizer.
• H280 Contains gas under pressure; may explode if heated.
• H314 Causes severe skin burns and eye damage.
• H330 Fatal if inhaled.

Key precautionary statements

• P220 Keep away from clothing and other combustible materials.
• P260 Do not breathe gas.
• P271 Use only outdoors or in a well-ventilated area.
• P280 Wear protective gloves, protective clothing, eye protection and face protection.
• P284 Wear respiratory protection.
• P304+P340+P310 IF INHALED: Remove person to fresh air and keep comfortable for breathing. Immediately call a POISON CENTER or doctor.
• P405 Store locked up.
• P410+P403 Protect from sunlight. Store in a well-ventilated place.

The federal OSHA PEL is a 5 ppm (9 mg/m³) ceiling that may not be exceeded at any time, from Table Z-1. NIOSH recommends a 1 ppm STEL, and Cal/OSHA has adopted the same 1 ppm STEL. The current ACGIH TLV is 0.2 ppm as an 8-hour TWA, based on lower airway irritation; older references list 3 ppm TWA and 5 ppm STEL, which ACGIH has since replaced. The IDLH is 13 ppm. Because symptoms can be delayed and the odor is not a reliable warning, use continuous gas detection wherever nitrogen dioxide can build up. State OSHA plans may set different limits.

• Appearance: Reddish-brown gas, or yellowish-brown liquid below 70°F; shipped as a liquefied gas
• Odor: Sharp, irritating, bleach-like odor
• Molecular weight: 46.0
• Boiling point: 70°F (21°C)
• Freezing point: 15°F (-9°C)
• Flash point: Not applicable (does not burn, but strongly supports combustion)
• Explosive limits: Not applicable
• Vapor pressure: 720 mmHg
• Relative gas density: 2.62 (much heavier than air)
• Specific gravity: 1.44 (liquid at 68°F)
• Water solubility: Reacts with water to form nitric acid

Inhalation

Irritates the eyes, nose and throat and causes coughing and shortness of breath. Nitrogen dioxide does not dissolve easily in the upper airways, so it reaches deep into the lungs and may cause only mild symptoms at first. Fluid in the lungs (pulmonary edema) can develop several hours later and can be fatal. High levels can also cause methemoglobinemia, which turns the lips and skin bluish. Entering freshly filled farm silos can cause "silo filler's disease" from nitrogen dioxide buildup.

Skin

Forms acid on moist skin and can cause burns. Contact with the liquid causes severe burns.

Eyes

Causes serious eye damage; the gas and liquid can burn the eyes.

Ingestion

Not a likely route for a gas. The liquid would cause severe burns to the mouth and throat.

Target organs

Eyes, respiratory system, cardiovascular system

Long-term effects

Repeated exposure can reduce lung function and cause chronic bronchitis. Severe acute exposures can be followed weeks later by bronchiolitis obliterans, a scarring of the small airways. ACGIH classes nitrogen dioxide as A4 (not classifiable as a human carcinogen).

Gloves

Acid-resistant gloves chosen with the manufacturer's permeation data. Nitrogen dioxide is a strong oxidizer, so confirm the material will not degrade.

Eyes and face

Non-vented chemical goggles with a face shield when handling cylinders or liquid. Provide an eyewash and quick-drench shower.

Respiratory

NIOSH lists only supplied-air respirators or SCBA for work exposures up to 20 ppm, and a pressure-demand SCBA for emergencies or unknown concentrations. Gas masks with suitable canisters are listed for escape only. Run this within a written respiratory protection program.

Clothing

Acid-resistant protective clothing. Responders to leaks need gas-tight chemical protective suits with SCBA. Remove contaminated clothing at once, since it can burn more easily after soaking up an oxidizer.

Store cylinders upright and secured, with valve caps on, in a cool, dry, well-ventilated, locked area away from heat, sunlight and combustible materials. Keep cylinder temperature below 125°F (52°C).

Use only in closed systems or with effective local exhaust. Nitrogen dioxide is also produced by many work activities, including gas and arc welding, brazing and cutting (see welding fume), diesel engines in enclosed areas, blasting, and fuming nitric acid. Treat freshly filled silos as hazardous confined spaces and test the air before entry.

Keep away from

• Combustible materials such as wood, paper, oil and fuels
• Water and moisture
• Ammonia, alcohols, hydrazines and other reducing agents
• Chlorinated hydrocarbons and carbon disulfide
• Aluminum powder, copper and copper alloys

• Evacuate the area and isolate it in all directions; call emergency responders.
• Do not enter without a positive-pressure SCBA and gas-tight protective clothing.
• Keep combustible materials away from the release.
• Stop the leak if it can be done safely and ventilate the area. If a leaking cylinder cannot be stopped, trained responders may move it to a safe open-air location.
• Absorb liquid with dry sand, earth or vermiculite (not sawdust or other combustibles) and place in sealed containers.
• Follow ERG Guide 124.

Suitable extinguishing media

• Nitrogen dioxide does not burn; use media suited to the surrounding fire
• Water spray to cool fire-exposed cylinders from a distance

Special hazards

A strong oxidizer that can ignite combustible materials and make fires burn hotter. Cylinders may rupture when heated. Fires involving nitrates and nitric acid can themselves give off nitrogen oxides. Firefighters must wear positive-pressure SCBA and full protective gear.

• OSHA Hazard Communication (29 CFR 1910.1200): Hazardous chemical. Labels and safety data sheets are required.
• OSHA Air Contaminants (29 CFR 1910.1000, Table Z-1): PEL 5 ppm (9 mg/m³) ceiling.
• OSHA Process Safety Management (29 CFR 1910.119): Highly hazardous chemical with a threshold quantity of 250 lb.
• CERCLA hazardous substance (40 CFR 302.4): Reportable quantity 10 lb; RCRA waste code P078.
• EPCRA Section 302 (40 CFR 355): Extremely hazardous substance; threshold planning quantity 100 lb; Section 304 reportable quantity 10 lb.
• EPCRA Section 313 / TRI: Not listed.
• Clean Air Act: Not listed under the 112(r) Risk Management Program (40 CFR 68.130). It is a criteria air pollutant under the national ambient air quality standards.
• DOT (49 CFR 172.101): UN1067 Dinitrogen tetroxide, Division 2.3 with subsidiary hazards 5.1 and 8; poison inhalation hazard.

• NIOSH Pocket Guide: Nitrogen dioxide
• OSHA Occupational Chemical Database: Nitrogen Dioxide
• NJ Department of Health Hazardous Substance Fact Sheet: Nitrogen Dioxide
• NOAA CAMEO Chemicals: Nitrogen Dioxide
• Airgas SDS: Nitrogen Dioxide
• NIOSH IDLH Value Profile: Nitrogen Dioxide
• Haz-Map: Nitrogen dioxide