Fig. 2. Deep dermal and partly III° nitric acid induced burn 1 hour after trauma, with intensified yellow staining on the second day and beginning demarcation from the 6th day under enzymatic therapy. The healing situation on day 26, 10 days after mesh-graft transplantation

Sulfuric acid

Sulfuric acid, also called dihydrogen sulfate according to IUPAC nomenclature [International Union of Pure and Applied Chemistry], is a compound of sulfur with the chemical formula H2SO4. It is a colorless, oily, nonflammable, very viscous and hygroscopic liquid with a penetrating odor. Sulfuric acid is one of the strongest acids and has a very corrosive effect. It finds wide application in the production of fertilizers, synthetic materials, paints, and paper. It is also used as an electrolyte in car batteries as well as in metal processing and in the preparation of food [4].

The mechanism of action of sulfuric acid depends on its concentration. In the case of diluted sul-

furic acid, the raised proton concentration has a caustic effect, similar to that of other diluted acids. Its effect upon contact with the skin mainly consists of local irritation and is therefore less hazardous than concentrated sulfuric acid [9]. The latter, even in small amounts, severely damages the skin and eyes and affects organic substances by dehydration under carbonization. Painful wounds develop that heal only very slowly. Surgical treatment i. e. excision and possible grafting, as well as conservative wound care is identical with protocols in thermal burns.

The inhalation of vapors of sulfuric acid can also result in inhalation trauma. The mists of concentrated sulfuric acid have a carcinogenic effect (IARC Group 1) [14]. Dose-effect relationships show the odor threshold at a concentration of 1 mg/m3, a concentration of 5 mg/m3 is subjectively intolerable and triggers the urge to cough, and the immediately lifethreatening concentration is 80 mg/m3. The MAC value is 0.1 mg/m3 [4, 11]. Sulfuric acid is likewise assigned to the hazard class C (caustic) and carries the risk phrase R35.

Hydrofluoric acid

The aqueous solution of hydrogen fluoride (HF) is called hydrofluoric acid. Hydrofluoric acid is a colorless, pungent-smelling liquid that as a strong acid generates heat upon reaction with many compounds and is thereby inflammable and explosive. It corrodes metal, glass and rock and is also used in a diluted form in the electronic and semiconductor industry as well as a detergent. A solution of 38.2% HF in water forms an azeotropic boiling mixture with a boiling point of 112 °C [4].

Hydrofluoric acid is a strong contact poison. Due to its quick resorption, the destruction of deeper tissue layers including bone is possible without the skin being visibly injured. A latent period of up to 24 hours until the appearance of first symptoms has been described for lower concentrations [4]. Excruciating pain following dermal exposure is a significant diagnostic feature. At higher concentrations, contact between hydrofluoric acid and the skin results in whitening of the skin, blisters, and colliquative necroses. A burn the size of a hand with 40% hydrofluoric acid is fatal due to the resorptive poisonous action. The IDLH value (Immediately Dan-

gerous to Life or Health) has been established at 25 mg/m3 (30 ppm) [9]. The MAC value is 1 ml/m3 or 0.83 mg/m3 [11].

Deeper skin penetration can be counteracted by repeatedly injecting the surrounding of the damaged tissue areas with 5–10% calcium gluconate solution. The distinct reduction of pain is an indicator for the amount to be injected and the frequency of injections. Therefore, local anesthetics should not be used. Upon contact with lower concentrations of hydrofluoric acid, the affected skin areas can also be treated with 2.5% calcium gluconate gel. The use of calcium chloride instead of calcium gluconate should be strictly avoided if calcium gluconate is not available, ice-cold 0.13% benzalkonium chloride compresses can be applied as an alternative. 2.5% aqueous calcium gluconate aerosols can be applied with 100% oxygen in the case of inhalation [4].

Fluoride ions are absorbed rapidly through the skin and eyes and thereby cause systemic involvement. The electrolyte balance is severely disturbed by the binding of calcium and magnesium; cardiac arrhythmias, ventricular fibrillation, and asystoly can result. Hydrofluoric acid also has neurotoxic effects. The warning effect of pain can therefore often occur with a delay of several hours. Involvement of the CNS can lead to coma and respiratory failure. Metabolic acidosis, acute kidney failure, and coagulation disorders can occur.

Caustic soda

Caustic soda is the term used for solutions of sodium hydroxide (NaOH) in water. Sodium hydroxide dissolves in water, thereby releasing heat, and forms an alkaline solution. Unimolar caustic soda (1 Mol NaOH (40g) in 1 liter) has a pH value of 14. It is one

Fig. 3. Superficial chemical burns caused by sodium hydroxide at 3 days, 3 weeks and 3 months after trauma under conservative wound care

of the most frequently used laboratory and industry chemicals [4].

Upon contact with concentrated caustic soda, the local caustic effect stands out, characterized by necrosis that quickly progresses to deeper layers of tissue. The tissue-damaging effect of caustic soda is due to its basic pH which causes protein compounds to dissolve. The specific picture of colliquative necrosis is attributed to the formation of hydrophilic alkali albuminates and saponification [9] (Fig. 3). Eschar formation does not take place. The extent of tissue damage depends to a large degree upon duration of exposure, concentration, pH value, dose, and the introduction of treatment measures. It should be noted that contact with the substance can remain unnoticed or underestimated at the beginning due to the delayed sensation of pain. The IDLH value (Immediately Dangerous to Life or Health) has been established at 10 mg/m3.

Quantitative data on skin resorption are not available. The absorption of systemically effective doses is not expected for concentrations that are not damaging to the skin. Numerous reports have been made about serious poisoning through ingestion of formulations containing sodium hydroxide (i. e. paint strippers, drain pipe cleaners). In case of resorption, the main systemic reaction consists of an influence on the blood pH value due to the release of hydroxyl ions. Homeostatic mechanisms can counteract an excess of sodium through increased excretion. Upon inhalation of sodium hydroxide, significant amounts may also become systemically effective [9].

Depending on the reaction conditions, serious eye irritation with swelling of the eyelid and mild corneal damage to severest damage to the conjunctiva, cornea, and sclera (clouding, perforation/ul-