When the envelopes were collected and the pail taken out, it induced a charge that made contact with a switch and then knocked the system off-line. While humans won't feel an ESD charge of under 3,000 volts, a charge of as little as 100V can damage many electronic components, and the majority of components can be damaged by a 250-V charge. Ditto for your production lines, where ESD can slip past quality control testing and cause direct or latent product failures. If it's time for you to update your wardrobe, consider natural fibers, such as cotton, over synthetics, and avoid pantyhose. Also, avoid rubber heels and soles.
Common activities can generate charges dangerous to equipment.