What is the fine-grained topic of the following text: Between 1993 and 2013, the Pipeline Hazardous Materials Safety Administration reports 108 "serious" incidents for natural gas transmission pipelines and their more than 80 explosions and fires in 2012 alone, which caused $44 million in damages. Only return the topic.
Incidents and damages caused by natural gas transmission pipelines from 1993 to 2013