The explosion_effect.zip file you have requested: Skins / Weapons / Half-Life 2: Enhanced Explosions Effect - 627.65kb is not available. Perhaps try browsing all files for the game Half-Life 2 and upload any files you want to share or are missing. This is the only information we could locate:
For more information on Half-Life 2, visit Halflife2.filefront.com This makes explosions in Half-life 2 more realistic and more visually pleasing. It's from the Real Explosion Effect by ToXiN.