How to Detect Nitric Acid Gas

Set up a nitric acid vapor detector on a surface that is near but not directly under the fume hood. Place it as close to the height of your head as possible, as nitric acid vapor is lighter than air.

Check the detector periodically while working. Depending on the type of detector being used, it will either indicate when nitric acid levels have reached a certain concentration or it will display the precise concentration (in parts per million, or ppm). Continue working if the nitric acid fume concentration is 2 ppm or less (the safe exposure limit set by the American Conference of Governmental Industrial Hygienists and the Occupational Safety and Health Administration).

Check the fume hood and increase ventilation if nitric acid concentrations are over 4 ppm (the short-term exposure limit set by the ACGIH and OSHA). Use a sealed, self-contained respirator if concentrations above 2 ppm cannot be avoided.

Evacuate the area if nitric acid concentrations are over 25 ppm, as these levels are immediately hazardous to health. Only properly trained and equipped personnel should enter the area of contamination.

Use your sense of smell in addition to detector technology. Nitric acid fumes have a very distinctive and irritating smell often described as being similar to horse urine. Increase ventilation if you can smell the fumes (the scent threshold for nitric acid fumes is 0.29 to 0.98 ppm, which is within the safety limits set by most regulators). Evacuate the area immediately if the smell becomes extremely "biting."

Evacuate the area immediately if you begin displaying any symptoms of nitric acid inhalation, such as skin, eye, nose or throat irritation (including rashes and ulcers), coughing, phlegm, shortness of breath, nausea, vomiting, diarrhea, or abdominal or chest pain.