It depends on the color indicator. Pure silica gel, molecular sieve and aluminum oxide are not classified as hazardous substances according to European Union legislation (Regulation EC No. 1272/2008). They do not require labeling according to EC Directive (67/548/EEC or 1999/45/EC). Silica gel is not classified as hazardous to health or the environment. Furthermore, they are non-flammable and chemically stable. No ecological problems are to be expected if handled and used properly.

If these adsorbents are used in aeration dryers, a color indicator is often applied. Especially with silica gels, various color changes are available that indicate the water content above a certain weight percentage. Some color indicators are classified as toxic and hazardous to health. Such color indicators also make these silica gels subject to labeling requirements.

Cobalt(II) chloride (CoCl2) was very often used as a color indicator in the past. When the silica gel has bound water, this indicator changes color from blue to pale pink to whitish; the hexaaqua complex ([Co(H2O)6]Cl2) is formed. On drying, this process is reversible.

To this day, aeration dryers with “blue gel” are used. And this despite the fact that cobalt(II) chloride is considered to be carcinogenic as well as teratogenic and possibly mutagenic. The substance was again included in the candidate list of substances of very high concern (SVHC) by the ECHA (European Chemicals Agency) on October 28, 2008. The entry was amended on June 20, 2011 to include the reproductive toxic properties.

Taking this into account, the EEA (Electricity Engineers’ Association of New Zealand), for example, in a handling recommendation issued to its members in April 2013, recommends the use of silica gel orange to minimize risks.

Silica gels with heavy metal-free indicators have been produced and used for several years. The indicators used are pH indicators, which belong to the organic dyes. These have the character of weak acids or bases. Thereby acid has a different color than the corresponding base. For silica gels, this means that the pH increases with increasing water content and the color changes from orange to green or white. This process is reversible and can be repeated.

When using Silica Gel Orange, attention must be paid to the indicator used and, in particular, the amount of it. For example, Silica Gel Orange is sold with approx. 2.5% methyl violet. This proportion of methyl violet is a cause for concern and is also classified as toxic. Manufacturers of silica gels who attach importance to sustainability as well as health-compatible and environmentally friendly products refrain from using such compositions. Among the pH color indicators, there are also harmless indicators. Since the color indicator has a significant influence on the quality of the silica gel, the exact mixing ratio is not specified by manufacturers with a claim to quality.

It is important that manufacturers provide essential information on use and compatibility in their safety data sheets in accordance with Regulation (EC) No. 1907/2006. must.