The deadly blaze that broke out at an assisted living facility in Massachusetts earlier this month was sparked accidentally by either a malfunctioning oxygen machine or, possibly, a resident smoking,

The state’s deadliest blaze in more than four decades has highlighted the lack of regulations governing assisted-living facilities that often care for low-income or disabled residents.

The deadly fire at an assisted-living facility in Fall River, Massachusetts, was accidental, but the cause is classified as undetermined.