(sigh) Looks like we're going to let facts get in the way here.

Urine contains no ammonia, unless you are REALLY REALLY seriously sick.

One of the by-products of the digestive systems of the bacteria that feed on urine residues is ammonia - hence the characteristic smell. The urine as it comes out is relatively sterile, and should be perfectly safe to use to spark off the heating pad.
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Knowing where you're going is NOT the same as knowing how to get there.