3-40 Table 3-3.—Common Sources of Electrostatic Charge OBJECT OR PROCESS MATERIAL OR ACTIVITY WORK SURFACES   WAXED, PAINTED, OR VARNISHED SURFACES   COMMON VINYL OR PLASTICS FLOORS   SEALED CONCRETE   WAXED, FINISHED WOOD   COMMON VINYL TILE OR SHEETING CLOTHES   COMMON CLEAN ROOM SMOCKS   COMMON SYNTHETIC PERSONNEL GARMENTS   NONCONDUCTIVE SHOES   VIRGIN COTTON* CHAIRS   FINISHED WOOD   VINYL   FIBERGLASS PACKAGING AND HANDLING   COMMON PLASTIC—BAGS, WRAPS, ENVELOPES   COMMON BUBBLE PACK, FOAM   COMMON PLASTIC TRAYS, PLASTIC TOTE BOXES, VIALS, PARTS BINS ASSEMBLY,   SPRAY CLEANERS CLEANING, TEST   COMMON PLASTIC SOLDER SUCKERS AND REPAIR AREAS   SOLDER IRONS WITH UNGROUNDED TIPS   SOLVENT BRUSHES (SYNTHETIC BRISTLES)   CLEANING OR DRYING BY FLUID OR EVAPORATION   TEMPERATURE CHAMBERS   CRYOGENIC SPRAYS   HEAT GUNS AND BLOWERS   SAND BLASTING   ELECTROSTATIC COPIERS PERSONNEL ITEMS   STYROFOAM COFFEE OR PLASTIC DRINK CUPS   PLASTIC OR RUBBER HAIR COMBS OR BRUSHES   CELLOPHANE OR PLASTIC CANDY, GUM OR CIGARETTE WRAPPERS   VINYL PURSES *VIRGIN COTTON CAN BE A STATIC SOURCE AT LOW RELATIVE HUMIDITIES (BELOW 30 PERCENT) Prevention of ESD Damage Certified 2M technicians are trained in procedures for reducing the causes of ESD damage. The procedures are similar for all levels of maintenance. The following procedure is an example of some of the protective measures used to prevent ESD damage. 1.   Before starting to service equipment, the technician should be grounded to discharge any static electric charge built up on the body. This can be accomplished with the use of a test lead (a single-wire conductor with a series resistance of 1 megohm equipped with alligator clips on each end). One clip end is connected to the grounded equipment frame, and the other clip end is