This is a tool that shows 25ish explosions and explosion like particles, as well as an area to add your own!
This will include two files- a .vmf and a .bsp, the VMF will show what particles are where and the BSP will allow them to be tested in game. The yellow line denotes areas for custom particles, dont bother with them unless you have edited the VMF as shown below.

Downloading-
1. download .zip file
2. extract to file
3. place .vmf in C:\Program Files (x86)\Steam\steamapps\common\Team Fortress 2\sourcesdk_content\tf\mapsrc
4. place .bsp in C:\Program Files (x86)\Steam\steamapps\common\Team Fortress 2\tf\maps
5. restart tf
6. you're good to go!

To find a good explosion for your map-
1. open BSP in game
2. press buttons till you find one you like
3. remember location relative to signs
4. open VMF
5. locate particle button in vmf
6. find info_particle_system
7. copy/paste into your very own map

To add/test with non standard particles
1. open VMF
2. buttons above yellow line are for other particles
3. edit particle systems for desired systems
4. test ingame
5. up to 5 can be tested at one time

This is not finished and will probably have more particles in the future, also I may have used Frontline stuff for some parts, so I suggest downloading that if you haven't already.