SILVER SPRING, Md. — The National Transportation Safety Board released its findings into the causes of the August 2017 natural gas explosion tragedy that killed seven people at the Flower Branch Apartments on Arliss Street in Silver Spring.

Here are the key takeaway points:

1) The gas explosion happened after a 1950's vintage vent in the building owned by Washington Gas became disconnected and a mechanical regulator did not stop the leak.

2) Washington Gas was never notified about a series of complaints about gas odors by either the landlord, Kay Management, nor the Montgomery County Fire Department. Both entities had received complaints from tenants.

3) Tenants complained at least six times about the odor of gas in the weeks and months leading up to the explosion.  But in most cases they called the landlord rather than 911 or Washington Gas. The NTSB recommends that anyone with concerns about gas odors should call 911 first, and the utility second.

4) Workers for Kay Management checked on the complaints but believed the odors were caused by painting in the building.

5) Kay Management changed the locks on the utility room door where the gas was leaking but did not provide a key to the Montgomery County Fire Department as required.

6) Firefighters responded to a 911 call for an odor of gas two weeks before the explosion. They found the door locked and could only partially pry it open. Firefighters did not detect gas and did not call in Washington Gas.