While all bulk cleaning will be carried out in a powered cleaner, hand cleaning will always be needed for fragile film or seriously dirty damaged film that must be cleaned prior to repair.
The usual method is as follows:
A non-abrasive cloth such as Canton flannel or a deep pile cotton plush or velvet should be thoroughly moistened with the film cleaning solvent. The cloth should then be folded in two around the film and the film drawn through the cloth at a sufficiently slow speed that the solvent evaporates before the film reaches the take up roll.
When the cloth dries it should be refolded in order to use a clean surface, re-wet with solvent and the operation continued.
Gloves must be worn to protect the hands from the solvents drying effect on the skin.
It is essential that this be carried out in an area specifically designed for this job with a high flow of extracted air across the film and away from the operator. All solvents used for this purpose are toxic to some extent, some more than others are. The level of the solvent in the atmosphere must be monitored and kept below the statutory concentration [TLV] for the compound. The area must be extracted by a grill or extract duct close to the film and cloth, and designed to draw air away from the operator into the extract system.
Manual cleaning should be done sparingly and only when essential, usually on very delicate film or very persistent individual marks [like old tape's cement, for example].
Mechanical cleaning machinery available today can clean almost anything with very low risks of damage and can be run slowly for maximum effect.