Tony Vassiliadis, the head nighttime custodian at Wellesley High School in Wellesley, Mass., demonstrates an electrostatic sprayer. During an actual cleaning, he would he would wear gloves and an N95 mask.

Tony Vassiliadis, the head nighttime custodian at Wellesley High School in Wellesley, Mass., demonstrates an electrostatic sprayer. During an actual cleaning, he would he would wear gloves and an N95 mask.