Which chemical compounds or mixtures are toxic

3. Dangers of irritating and corrosive substances and mixtures

3.1 Health hazards

Corrosive substances can quickly lead to severe tissue damage and serious, permanent damage to health. Basically, alkalis are to be regarded as even more dangerous than acids. Information on the respective material properties is e.g. B. to be found in the respective safety data sheet.

Damage to health from irritating and corrosive substances can occur through:

  • Skin contact (skin damage),
  • Eye contact (eye damage),
  • Inhalation (damage to the airways and lungs)
  • Ingestion (damage to lips, oral cavity, throat, esophagus, stomach).

The extent of tissue damage is i.a. depending on

  • the chemical properties of a substance,
  • the amount of substance acting,
  • the active substance concentration as well as
  • on the duration of the action.

3.1.1 Effects on the skin

The effects on the skin can range from slight skin irritation (reddening of the skin) to severe damage to the skin and the underlying tissue (necrosis).

3.1.2 Effect on the eyes

The eyes are particularly endangered. Splashes of alkalis and acids can cause irritation, but also severe burns that lead to blindness.

3.1.3 Effects on the respiratory tract

Inhaling gases, vapors and aerosols of irritating and corrosive substances can lead to irritation of the respiratory tract, but also to severe, acute illnesses. In severe cases, chronic lung diseases can also follow.

The complaints are acute or creeping z. B. in the form of irritation of the eyes and the nasopharynx, cough and sputum.

Shortness of breath as a possible sign of a serious illness (toxic pulmonary edema) can occur immediately, but also after a longer period of time without symptoms (e.g. 24 hours).

3.2 Hazardous chemical reactions

Irritant and corrosive substances belong to different groups of substances with different chemical properties. When working with the following groups of substances, dangerous chemical reactions can lead to accidents:

3.2.1 Acids and bases

Heat development when thinning

When making up solutions or diluting acids and alkalis, so-called dissolution heat is released. The released heat of dissolution can lead to sudden boiling over and splashing of the hot, caustic solution. Because of this danger, which is often underestimated, particular caution is required during such processes (see 5.2.3 and 5.3.1).

Heat development when mixing

Acids react with alkalis, releasing heat of neutralization. As with thinning, the hot, aggressive solution can suddenly boil over and splash.

Oxyhydrogen formation and corrosion when reacting with light metals

Acids and alkalis dissolve light metals such as aluminum and zinc with the formation of hydrogen (oxyhydrogen). In the presence of an ignition source, the hydrogen reacts explosively with the oxygen in the air.

3.2.2 Active chlorine products

Risk of release of chlorine gas

A typical representative of this product group is sodium hypochlorite (also known as bleach), which contains sodium hypochlorite (NaOCI).

If sodium hypochlorite is mixed with acid, large amounts of chlorine are quickly released. Chlorine is a pungent-smelling green-yellow gas and is quickly fatal in the air in amounts of only 0.5–1% on mammals and humans! Even hours after inhalation, chlorine can lead to pulmonary edema (water in the lungs) and shortness of breath.

In addition to the reaction with acids, other dangerous reactions of sodium hypochlorite solution are known:

  • Strong reducing agents, e.g. B. Light metals such as aluminum or zinc from system parts lead to strong heat generation,
  • Oxidizing agents such as nitric acid or potassium permanganate lead to the release of dangerous gases (chlorine or oxygen with an oxidizing effect),
  • Ammonium hydroxide solutions, ammonium salts and various organic substances lead to violent, sometimes explosive reactions,
  • Thermal decomposition when heated above 40 ° C.

3.2.3 Active oxygen products

Risk of decomposition with development of heat and release of oxygen

Typical representatives are hydrogen peroxide and peracetic acid. Hydrogen peroxide (H.2O2) is unstable and slowly disintegrates into water and oxygen after long periods of storage. This decomposition process is accelerated when heated or in the presence of a large number of substances so that larger amounts of oxygen (oxidizing!) Are quickly released with high heat generation. Even small amounts of contaminated contaminants can initiate and accelerate the decomposition process.

Peracetic acid (PES), also known as peroxyacetic acid, is usually sold as a mixture of 5–15% peracetic acid, hydrogen peroxide, acetic acid and water. PES is also unstable and breaks down into acetic acid and oxygen. As with hydrogen peroxide, this decomposition process is caused by the action of heat and impurities such as B. Rust accelerates considerably (see also ASI 8.03 “Handling peracetic acid”).

Due to the risk of contaminants being brought in, hydrogen peroxide and peracetic acid may only be stored in the original container and must not be refilled. No residues may be returned to the original container.

3.2.4 Nitric acid

Risk of gas formation

Nitric acid is very aggressive and reacts with a large number of substances (including metals), releasing so-called nitrous gases. Nitrous gases are a mixture of different nitrogen-oxygen compounds. The fumes are red-brown, have a pungent odor, and are irritating and toxic.

3.2.5 hydrofluoric acid

The hydrofluoric acid (hydrofluoric acid), which is still used - mainly for welding and soldering work in the form of pickling paste - is of particular importance in terms of its dangerousness. The acid is not very strong, but extremely aggressive and also poisonous. It can penetrate deep into the tissue and lead to wounds that are difficult to heal. Anyone who cannot do without hydrofluoric acid must avoid skin contact in any case and use special gloves (fluororubber, Viton®). For pickling paste containing hydrofluoric acid there are substitute processes in many cases, e.g. B. the use of handheld electrolysis devices together with less dangerous phosphoric acid-based agents.