It's crashing me so I'll work it now... You need change 'normal' to a vector - you have no idea what value the 'normal' contains.

EDIT* Ok new to me .. Maybe you can use effect_sprite(STRING* image, EVENT func, var number, VECTOR* pos, VECTOR* vel) for that effect.

EDIT2* Also you need time_step in the particle number.
effect(p_explo1,100*time_step,my.x,vector(10,10,20));