Secondary Drowning is a portion of the National Pool Lifeguard Qualification. The information in the Wikipedia is slightly out of date following recommendations by the World Congress on Drowning (2002) which were adopted by ILCOR (2005). For further information see a summary here: http://manchesterlifesaving.org.uk/content/view/95/43/ The effects of Secondary Drowning can occur upto 72 hours after the drowning incident. I have deep concerns that the child was on the bottom of the pool for 30 seconds. The human body is fairly bouyant, and doesn't like sinking unless the lungs and stomach are filled with water. But more importantly, if the Lifeguards were doing their job effectively, that's about 20 seconds too long! That's not including the time it took for his body to sink. Regards.