Safety Issues with Pyridine Ring Construction

Normally amines/ammonia form the source of the ring nitrogen. Occasionally Hydrazine or more often hydroxylamine are encountered as N synthons.

Concentrated solutions of hydroxylamine in water can be explosive and should be handled appropriately.
https://www.csb.gov/concept-sciences-hydroxylamine-explosion/

Hydrazine can decompose violently in the presence of metal catalysts and is a suspect carcinogen.

This material is labelled as a skin sensitizer and a carcinogen under EU REACH regulation and is on the substances of very high concern (SVAC) list.
https://echa.europa.eu/substance-information/-/substanceinfo/100.005.560