Pyrotechnics and explosives on a plane
For departures from the United States, TSA bars pyrotechnics and explosives from both carry-on and checked baggage. A small charge, retail packaging or placement inside another object does not change that result. Realistic explosive props have a separate prohibition even when inert.
Party snaps and fireworks
Party poppers, bang snaps, firecrackers and fireworks are all barred from both bags at a US checkpoint. The same applies to English Christmas crackers containing a party snap and to bear bangers. Do not assume a small packet or a holiday label creates an exception.
Initiators and explosive devices
A blasting cap is an initiator, not an ordinary metal fitting. TSA also lists dynamite and hand grenades as prohibited in both bags. Removing these parts from a kit or moving them to checked baggage does not make them acceptable passenger baggage.
Inert props and lookalikes
TSA prohibits realistic explosive replicas and realistic replicas of incendiary devices in both bags. An inert grenade-shaped prop still needs to be treated as a replica. A decoration that does not resemble such a device is a different item; assess its own materials and any attached battery or liquid separately.
Source: TSA: What Can I Bring?.