Self-indicating (blue) Silica Gel

27. (2002)

Self-indicating (blue) silica gel has been a common desiccant in laboratories for many years. The indicator is cobalt (II) chloride, present in a concentration of 0.5 to 1% weight for weight on the amorphous silica gel. The moisture sensitive material changes from blue to pink as it absorbs moisture. Heating can regenerate the desiccant.

The common laboratory routes of exposure to self-indicating (blue) silica gel are via contact with the skin and inhalation of dust. The material is generally granular since it is makes a better desiccant. Dust can be created from the desiccant by crushing, abrasion, rubbing or otherwise powdering the material. It is the cobalt (II) chloride in the desiccant that is of a health concern.

The dust is capable of drying the skin and may cause irritation and dermatitis. Allergic inflammation may occur following exposure to cobalt, usually exhibited as red patches. If contact occurs to un-gloved hands, wash with soap and water. A moisturising cream may be of benefit to re-hydrate the skin.

Inhalation of the dust is slightly discomforting/irritating to the upper respiratory tract. Inhalation of dust may aggravate a pre-existing respiratory condition (asthma, emphysema, bronchitis etc). Respiratory sensitisation may result in allergic/asthma like responses; from coughing and minor breathing difficulties to bronchitis with wheezing and chest tightness. Cobalt (II) chloride has been revealed to be a confirmed animal carcinogen at relatively high doses. A European Commission Directive (98/98/EC) reclassified cobalt chloride as a potential carcinogen by inhalation. The International Agency for Research on Cancer (IARC) indicates there is limited evidence for carcinogenicity of cobalt (II) chloride in experimental animals, and has assigned cobalt and cobalt compounds as possibly carcinogenic to humans (group 2B).

It needs to be remembered that the EC directive was for the pure chemical, whereas the silica gel contains 1% w/w and is within the gel material. The health risk associated with self-indicating (blue) silica gel therefore only exists when handling the material and exposure to the dust.

It is recommended that -

• Alternative to the self-indicating (blue) silica gel are available and should be purchased/used when possible. An appropriate replacement desiccant is the self-indicating (orange) silica gel available from most laboratory chemical suppliers.
• Self-indicating (blue) silica gel should be handled in the fume cupboard whenever there is a risk of generating dust. For example, pouring into desiccator jars, heating vessels. The risk of exposure to a small dust cloud that may result when a desiccant jar is opened is considered insignificant. If there are concerns regarding the desiccant or chemicals in the jar, the jar should be opened in the fume cupboard.
• Dusty self-indicating (blue) silica gel should be gradually removed from service. Material should be placed in a tough plastic bag and sealed. Disposable is via the appropriate waste contractor.
• Material should not be powdered/crushed or handled in any way likely to cause significant dust exposure.

Reference:

1. CHEMWATCH Material Safety Data Sheets — Cobalt (II) chloride and self-indicating (blue) silica gel.
2. Various commercial web sites related to silica gel.
3. IARC agents and summary evaluations - http://monographs.iarc.fr/

For further information contact:
OHS Officer, e-mail: OHS.Officer@anu.edu.au