Conclusion
The Boston area experienced 62 events in 2021 (down from 212 in 2018). As of 2022, local utility company Eversource is replacing 38,000 maintenance hole covers, starting in high-traffic areas, with a safer design. A rail allows the cover to lift up to 4 inches (100 mm) and let gases escape, but prevents it from flying into the air and damaging buildings or cars or injuring pedestrians. In some places where road salt is not a concern, the covers have vents to let gases escape. To prevent and mitigate safety problems, the company is also installing monitoring equipment to detect dangerous gases and fires, and increasing inspection frequency.[15]