Like with all custom particles, they need to be listed in a manifest file named after your map. For example: if your map is named pl_tf2maps, there needs to be a text file named "pl_tf2maps_particles.txt" inside the "maps" folder containing this code:
Code:
particles_manifest
{
"file" "!particles/wartime_barrel_explo.pcf"
}
Also make sure that the particle file itself is located inside "custom/foldername/particles/".