The Group 5A hydrides are especially toxic gases. The gas from arsenic is arsine with an earlier Merck index stating a “dangerous” level by inhalation of 0.5 ppm. The hydride gas from phosphorous is phosphine gas with the same Merck Index giving 8 ppm as being lethal in hamsters. Antimony’s hydride gas is stibine with the lethal concentration in air for mice as 100 ppm.The later Merck Index, 13th Edition, does not give lethality levels for these hydride, but for only the stibine gas at 100 ppm.The lowest molecular weight Group 5A hydride, ammonia, from nitrogen has roughly a 5000 ppm LD50 in mice exposed for one hour as given on Wikipedia. Therefore, ammonia is not quite as lethal as the other three hydrides mentioned.