Hazards are classified according to the concentration of the the acid. At concentrations between 5% and 20%, it is given the Risk Phrase R34 'Causes burns'; above 20% it is given the Risk Phrase R35 'Causes severe burns' and above 70% it is also classified as Oxidising R8 'Contact with combustible material may cause fire'. These classifications are according to the current CHIP Regulations and will be valid until 1 December 2010. After this time the classificiation of the acid hazards will change to the CLP Regulation 1272/2008 and be according to GHS (the Globally Harmonised System). Limits for Corrosivity will remain the same but the Oxidising concentration drops to 65%; also the symbols and phrases change.
- At 65% and above, the classification is 'Oxidising Liquid 3, with Hazard Statement H272'
- Between 5 % and 20%, the classification is 'Skin Corrosion IB, with Hazard Statement H314'
- At 20% and above, the classification is 'Skin Corrosion 7A, with Hazard Statement H314'
- From the above it is clear that the acid is still hazardous even at dilute concentrations. HNO3 will cause serious burns and skin tissue damage if left in contact without washing. More concentrated solutions will produce an immediate burning sensation on contact with skin, while dilute forms cause irritation. If skin contact has occurred, it is advisable to rinse the area well with water and seek medical assistance in serious cases.
Superficial HNO3 burns attack the top layer of skin and cause it to turn a yellow-brown colour; this is due to the reaction with Keratin. Eye contact should be avoided as serious damage can be caused especially with more concentrated solutions. Nitric Acid hazards include blindness, if concentrated forms are in contact with the eye.
Oxidising properties of Nitric Acid
Due to the Oxidising properties of Nitric Acid above 70%, it is important to store away from flammable and combustible materials as it may promote the spread of fire. In this case, fire fighters must wear self-contained breathing apparatus and full protective clothing. Solutions begin to generate fumes as the concentration increases. Certainly above 65% these will be Corrosive to the respiratory system if inhaled, so fume extraction should be used when handling.
Toxic fumes or vapours wil be produced in the case of fire from the formation of Nitrous gases NOx. Nitric Acid hazards include inhalation of acid vapours which will cause coughing and may lead to formation of oedemas in the respiratory tract.
Personal Protctive Equipment (PPE)
The correct Personal Protctive Equipment (PPE) should always be worn when handling HNO3. For example, gloves, eye or face protection, suitable protective clothing capable of resising acid contact and, if necessary, respiratory protection. It is important to check with the manufacturer of the PPE for its compatibility with Nitric Acid before use. Always provide eye wash facilities and if handling larger amounts, a safety shower. Do not eat, drink or smoke when using HNO3. When Nitric Acid is ingested it will cause severe internal burns and, if taken in large amounts, could be fatal.
HNO3 should not be discharged to the environment as it may have serious ecological effects. It can change the pH of water systems and contaminate groundwater and soil, therefore should always be disposed of as Hazardous Waste. Nitric Acid is miscible with water and will spread in water systems. When being transported, it is classed as Hazardous substance and must be carried in accordance with ADR Regulationas or other applicable legislation. The UN number is 2031 and it is classified as Class 8, Corrosive substances.
Acidic hazards include some hazardous reactions of the Acid. As it is a strong acid, it will react exothermically with alkalis. It is a powerful oxidising agent and may produce explosive reactions with organic materials. In the present of other Oxidising agents, such as Hydrogen Peroxide, it is possible that a violent reaction may occur which produces large amounts of heat and Nitrous gases. This would occur at acid concentrations above 35%.
Other Nitric Acid hazards relating to its reaction with other substances include:-
- Concentrated Nitric Acid reacts with Cuprous Oxide to produce Nitric Oxide, NO.
- Ethanol reacts violently with Nitric Acid to produce Nitrogen Dioxide, a brown gas.
- Oxides of Nitrogen are Toxic gases.