[OT: Home Improvement] rotting brick and range hoods - there's red sand on my stove

[mattkime]

I'm living in an apt that was renovated about a year ago and build in the 1930s. there's brick behind my stove. red sand/dust collects from what appears to be (and for lack of a better name) rotting brick. when i turn on the vent some of the red dust COMES OUT. This would be disastrous if you turned it on during a meal.

has anyone seen something like this before? what causes it and what can be done?