Event raids are raids that usually correspond with a special event that 5th Planet is having for DotD. Like world raids, they do not have a health bar and are only "defeated" when the timer runs out. Also like world raids, the goal of event raids for each player is to deal enough damage to qualify for a number of chances to get the desired loot. The number of pieces of loot in each quality tier increases with damage done with minimum damage requirements for each tier.
The cap on the number of players which can join a event raid is set arbitrarily high so that all players on a given server may join.