TAB D - Overview of Inhibited Red Fuming Nitric Acid and Related Health Hazards

The following information was extracted directly from a document prepared by the Chemical Propulsion Information Agency.[209]


Inhibited red fuming nitric acid (IRFNA), known as type IIIB fuming nitric acid in the US, is used as a liquid propellant rocket engine oxidizer. It is light-orange to orange-red in color, clear, strongly fuming, and evolves toxic nitric acid vapor and yellow-red vapors of nitrogen oxides. Fuming nitric acids are unstable releasing nitrogen dioxide, nitric oxide, and nitric acid mist into the atmosphere. Fuming nitric acids are highly corrosive oxidizing agents and will vigorously attack most metals. They also react with many organic materials resulting in spontaneous combustion. IRFNA has the following chemical composition (by weight) and physical properties:

Nitrogen dioxide (NO2) 13-15%
Water (H2O) 1.5-2.5%
Nitric acid (HNO3) 81.6-84.8%
Nitrate solids .04% max
Hydrogen fluoride inhibitor .7%
Boiling point 337.34 K
Freezing point 221.15 K
Density (liquid) 1.55 Mg/m3 at 298.15 K
Vapor pressure 1.38 kPa at 255.35 K
kPa at 298.15 K
kPa at 310.95 K
kPa at 337.55 K


Health Hazards and Symptoms of Exposure

Toxicity: IRFNA, in contact with any surface of the body (skin, mucous membrane, eyes), destroys tissue by direct contact. It stains the skin or surface a yellow or yellowish-brown and sustained contact results in a chemical burn. The vapors are highly irritating and toxic to the respiratory tract. Immediately after exposure to dangerous concentrations, there may be coughing, increased respiratory rate, asthmatic-type breathing, nausea, vomiting, and marked fatigue. A fatal pulmonary edema may develop.

Special Medical Information: Exposure to dangerous atmospheric concentrations of the oxides of nitrogen may cause spasm of the terminal bronchioles and disturbances of reflexes causing respiration. Circulatory collapse may ensue, or the symptoms may subside and reappear several hours later with the onset of pulmonary edema. Certain signs indicating that severe lung damage has occurred may appear within the first few hours. These are an increase in platelets in the venous blood, often as great as 60 to 100 percent, a decrease in blood pressure, and an increase in the hemoglobin content of the blood. Spasmodic cough and dyspnea appearing several hours after the exposure are evidence of the development of pulmonary edema; bronchopneumonia may be a complication. IRFNA contact with the eyes causes irreparable damage within seconds.

Chronic Exposure: Chronic exposure to low concentrations of the oxides of nitrogen may produce wearing down and decay of the teeth, pulmonary emphysema, and chronic inflammation of the respiratory passages, often with ulceration of the nose or mouth.

Exposure Limits

Threshold Limit Value - Time Weighted Average (TLV -TWA): A threshold limit value for IRFNA itself has not been established, however, the atmospheric threshold limit values for its more toxic components are as follows:

Nitric acid mist 2 ppm (5 mg/m3)
Nitrogen dioxide 3 ppm (6 mg/m3)
Nitric oxide 25 ppm (30 mg/m3)


Threshold Limit Value - Short Term Exposure Limit (TLV -STEL) values are as follows:

Nitric acid mist 4 ppm (10 mg/m3)
Nitrogen dioxide 5 ppm (10 mg/m3)
Nitric oxide 35 ppm (45 mg/m3)


Emergency exposure limits for nitrogen dioxide are set as follows:

10 minutes at 30 ppm (54 mg/m3)
30 minutes at 20 ppm (36 mg/m3)
60 minutes at 10 ppm (18 mg/m3)


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