Cleaning small parts and portable equipment with solvents, either using an automatic device or manual cleaning, is a potentially extremely hazardous task relative to static generation and spark ignition of solvent vapors. Significant static electricity charging can occur during cleaning by contact and separation resulting from the following activities:
- Solvent spraying, which can involve high liquid velocities
- Stream impingement on the object being cleaned
- Misting
- Rubbing
- Brushing
Using a solvent-soaked wiper to clean a part shares these static generation problems. When these activities are coupled with the use of a poorly conductive flammable solvent, as is often the case, the result can be a serious incident.
WARNING!! The use of a nonconductive Class II (combustible) cleaning solvent such as mineral spirits in a vessel that contains vapors in the flammable range can generate enough static electricity to ignite the flammable vapors.
When it is necessary to perform manual cleaning of parts, etc., with Class I solvents, the following are some precautions that should be considered:
- Use conductive solvents (conductivity greater than 10,000 picosiemens per meter)
- Use natural bristle brushes for cleaning. Natural bristles include materials like Palmyra, Tampico, Bamboo, Horse Hair and Hog Bristle. Brushes made with bristles of synthetic polymeric materials such as polyethylene, polypropylene, nylon, polyester, etc., should be PROHIBITED
- GROUND the conductive objects being cleaned
- Maintain GOOD VENTILATION to remove or dilute solvent vapors to prevent the buildup of a flammable vapor/air mixture, keeping in mind that ventilation may fail or otherwise be only partially effective in keeping the flammable concentration below the lower flammable limit
- If a low conductivity solvent has been used, allow objects that have been cleaned to sit undisturbed for 10 minutes, to allow for relaxation of accumulated charge.