The metal salts form a complex with chloride ions. Depending on the water concentration, the complex is formed with water or chloride ions.6 At high humidity, the complexes are formed with water, which have a different color than the complexes with chloride ions. A frequently used metal salt is copper sulfate. It is contained in the silica gel orange-green. The moisture indicator of the Orange-Green Silica Gel probably contains a salt with chloride ions.
The concern of silica gels depends on the moisture indicators. Pure silica gel is not hazardous to health. The moisture indicators of the silica gels used by Giebel FilTec GmbH are all made of metal salts. The silica gel blue-pink, with a moisture indicator made of cobalt dichloride, is considered to be the most harmful to health. The REACH regulation classifies it as a special concern because it is carcinogenic and toxic to reproduction. Copper sulfate, which is contained in silica gel orange-green, poses a health hazard if swallowed. It causes skin irritation and eye discomfort on contact. When disposing of the product, its harmfulness to aquatic organisms must be taken into account. Silica gel orange colorless, due to the ammonium iron (III) sulfate, causes skin irritation and eye discomfort. However, the content of copper sulfate and ammonium iron (III) sulfate in the silica gels is so low that there is no danger and it does not have to be stated in the safety data sheet.