Interesting article. I know that Iyengar is not a proponant of Kapalabhati or Bhastrika. He does teach it in his books but only for a few breaths at a time, maybe 10 breaths in a cycle. Personally when I was young I would practice it for up to 10-15 minutes at a stretch with no ill effects but I was young and healthy and was very well practiced in asana. I say no ill effect but also no real deeper effect as I have found in AYP SB pranayama. It is invigorating and helps wake up the circulation but from my experience 1 minute should be sufficient to get benefits. All pranayama can be dangerous. Incorrect practice of breath retention can cause stress to the nerves and possibly effect the heart. Pranayama needs to be practiced with great sensitivity, regularity and care. It is much better to underdo that overdo.That said, I believe that considering the limitations of the lack of direct personal contact that Yogani has been doing an outstanding job of teaching pranayama to as wide an audience as possible. At that point, the responsibility falls on the practitioner to pay very close attention to the messages that their own body sends during practice and self pace accordingly. As for other teachers, I can't say and I personally have never heard of any deaths ascribed to yoga practices. I have however many times in my life had to correct my pranayama practice due to ill effects that I could feel in the form of emotional or neurological stress that usually quickly responded to corrections in practice. The breath is a very subtle and very deep and very core to our life itself and needs to be worked with in the most sensitive way possible in order to get benefit.