Any closeable item (book, box, bottle, chest, coffer, coffin, door, drawer, and so forth) can be warded by a fire trap spell. The spell is centered on a point selected by the spellcaster. The item so trapped cannot have a second closure or warding spell placed upon it (if such is attempted, the result is 25% first spell fails, 25% second spell fails, or 50% both spells fail).
A knock spell does not affect fire trap in any way - as soon as the offending party enters or touches the item, the trap discharges. Thieves and others have only 1/2 of their normal chance to detect a fire trap (by noticing the characteristic markings required to cast the spell). They have only 1/2 of their normal chance to remove the trap (failure detonates the trap immediately). An unsuccessful dispel does not detonate the spell.
The caster can use the trapped object without discharging it, as can any individual to whom the spe11 was specifically attuned when cast (the exact method usually involves a keyword).
When the trap is discharged, there is an explosion of five-foot radius from the spell's center; all creatures within this area must roll saving throws vs. spell. Damage is ld4 points plus 1 point per level of the caster; half this (round up) for creatures successfully saving. (Underwater, this ward inflicts half damage and creates a large cloud of steam.) The item trapped is not harmed by this explosion.
To place this spell, the caster must trace the outline of the closure with a bit of sulphur or saltpeter and touch the center of the effect. Attunement to another individual requires a hair or similar object from that person.