It might be required to import the class to avoid errors.
import crafttweaker.world.IExplosion;

To create an IExplosion object, you must obtain it from an IWorld and call it with any of these three methods:

• world.createExplosion(IEntity, double, double, double, float, bool, bool);
• world.performExplosion(IEntity, double, double, double, float, bool, bool);
• world.performExplosion(IExplosion);

ZenGetter	ZenSetter	Type	Description
ZenGetter world	ZenSetter ​	Type IWorld	Description The world of the explosion.
ZenGetter placedBy	ZenSetter ​	Type IEntityLivingBase	Description The entity that initiated the explosion. If the explosion was caused by TNT, the entity is the entity that placed down the TNT, if applicable. Can be null.
ZenGetter position	ZenSetter ​	Type Position3f	Description The position of the explosion.
ZenGetter affectedBlockPositions	ZenSetter affectedBlockPositions	Type IBlockPos[ ]	Description A list of block positions that the explosion affects. May be null/empty before doExplosionA() is called.
ZenGetter playerKnockbackMap	ZenSetter ​	Type IVector3d[IPlayer]	Description A map of players in the explosion area mapped to their respective knockbacks taken from the explosion.

• clearAffectedBlockPositions() - clears the list of affected block positions
• onExplosionStart(IWorld world) - returns a bool that is the result of the ExplosionStart event in the specified world, so this should be called if you want to use logic to possibly cancel your explosion before detonating it manually.
• doExplosionA() - performs the first part of the explosion; this includes entity damage, entity knockback, and affectedBlockPositions assignment.
• doExplosionB(bool spawnParticles) - performs the second part of the explosion; this includes sounds, particles, block destruction/dropping, and fire creation.