(WSB photos)

9:55 AM: If you’re wondering about the SFD/SPD response in the 8800 block of 35th SW, Seattle Fire says they’re “investigating a possible chemical substance in apartment building” and advising people to stay away from the area. Updates to come.

10:06 AM: Our crew reports 35th is blocked between Henderson and Trenton; this is happening in an apartment building nearer to Henderson than Trenton. SFD confirms one person was found dead in the building.

10:24 AM: The Medical Examiner has arrived at the scene but before they can handle the death, SFD crews are still working on the unspecified hazardous-materials situation. While 35th remains blocked, police are allowing buses through.

10:42 AM: SFD is still dealing with the scene, with hazmat gear and washdown stations. SFD’s public information officer Kristin Tinsley is there so we should get some updates soon. And the helicopter, if you’re wondering, is a TV station.

11:01 AM: Just briefed, by Tinsley and SPD PIO Det. Mark Jamieson. (video added)

This started – as a commenter noted – as a “welfare check,” a call for police to check on someone who hadn’t been heard from in a while. Officers who found the dead person had clearly been exposed to something – hazmat crews are in the unit still trying to figure out what. The two officers have been taken to a hospital to be checked out. Nearby residents aren’t believed to be in danger but for now they’ve been asked to keep their doors/windows closed as a precaution.

11:22 AM: More information. The substances were primarily ammonia and chlorine bleach. The person found dead was a woman.

The response is mostly wrapping up now. That’s the other TV helicopter over the area now, by the way.

12:02 PM: SDOT says all lanes of 35th SW have reopened.