Guarino and two others (plaintiffs) died of gas asphyxiation and five others were injured when they entered a sewer tunnel without masks to answer the cries for help of their crew leader, Rooney. Rooney had left the sewer shaft and entered the tunnel to fix a water leakage problem. Having corrected the problem, Rooney was returning to the shaft when he apparently was overcome by gas because of a defect in his oxygen mask, which was manufactured by Mine Safety Appliance Company (defendant). Plaintiffs brought this action against the defendant for breach of warranty, and defendant raised the defense of plaintiffs' voluntary assumption of the risk. Explain who will prevail.