The developmental risks defence: If scientific and technical knowledge at the time of producing the product into circulation was not capable of discovering the existence of the defect the defendant will not be liable. This was the case in Roe v Minister of Health. The claimant was left paralysed after microscopic cracks in glass, where his anaesthetic was stored, became contaminated. The defendants were not liable as there was known way of knowing their procedure for storing anaesthetic was dangerous until the claimant revealed the risk.