So this is the general idea i have. You got 3 Fuel Tank Rows that each blow up one after the other. For this i have created this:

As you can see, we got the 3 Rows and the switchers switch from one row to the next. The idea being that i feed this Geometry into the Pop net and control when the Bursts happen there with an expression for the Birth Rate. In my case i used this expression:

if($F==1,1,0)||if($F==11,1,0)||if($F==21,1,0)

And this does work. The Particles appear as intended one row after the other. Even more important, when i click on the "Volume Rasterize Attributes" node, i can see the 3 Seperate Bursts happening.

But now the problems start. The Pyro Source node doesnt care that much what i want. It only creates a Fireball for the first row, everything after that gets ignored. As seen here:



The Particles appear, but the Solver / Source dosnt use them.

Now initially i though that maybe the Particles in Row 2 and 3 dont have any Attributes. But this is not true, they have them and i even went as far as to make 3 node trees for the 3 Rows to make sure all have Attributes.

After a bit of trial and error, o figured out that the problem is in the switchers. For some reason, Houdini dosnt like it when i switch around the Geometry. I know this because lets say i directly connect the Geometry of Row 2 to the Pyro Source, well then i get a result.

So the error has to be in those Switching Nodes, but i just dont know where or why.

Maybe the Expressions are bad ? I used "$F>20" to tell it when to switch. And again, this works with the Particles.

So, any idea what could be the error here ?

It could be related to the pyro bounding box. If fuel exists outside the domain, it's can't be ignited. Maybe use the entire bounding area of all three switches activated at once to determine the size the pyro box needs to be..? Merge all those merges and drop down a bound.

since you are using H18.5 maybe you should try the new burst sourcing tools
https://vimeo.com/473044209 [vimeo.com]

shouldn't it be this simple ?

if your brain likes the use of multi switch like you have in your orig setup (rather than the nested if), here's how: