Electric bicycles, which environmentalists and Democratic lawmakers have touted for their zero-carbon output, are facing increased criticism over the rising number of tragic incidents involving their batteries.

According to the National Fire Protection Association (NFPA), so-called e-bikes are powered by lithium-ion batteries which are prone to fires or explosions. And as e-bikes continue to become more popular — the global e-bike industry is expected to grow nearly 200% to an estimated value of $118.7 billion by 2030, according to Allied Market Research — more cities nationwide are facing rapidly-increasing numbers of battery fires.

“The majority of lithium-ion battery fires that fire departments across the country are dealing with involve these micromobility devices,” Matthew Paiss, a technical advisor in the Battery Materials & Systems group of the Pacific Northwest National Laboratory, told the NFPA Journal last year.