The The Butcher's BBQ Pack Add-on for PAYDAY 2 has 4 achievements.
Set an enemy on fire and kill him with the "Motherforker" melee weapon. Unlocks "The Gas Mask" mask, "Candlelight" material and "Flammable" pattern.
Kill 10 enemies within 10 seconds using the Piglet Grenade Launcher without using Incendiary rounds. Unlocks the "Firefighter's Helmet" mask, "Burn" material and "Flamer" pattern.
Have 10 enemies burning simultaneously. Unlocks the "Graug" mask, "Coal" material and "Fireborn" pattern.
Set a Bulldozer on fire for at least 10 seconds. Unlocks "The Chef" mask, "Toast" material and "Hot Flames" pattern.