Manufacturing Engineer and Factory Safety Engineer Discusses Bungee Cords

Manufacturing engineer discusses bungee cord safety from a safety engineering view point. Stretching a bungee cord imparts a significant amount of potential energy into the system that can be released and make the end hook a dangerous projectile. There are safety warnings on most cords; however, these are often ignored or torn off. It has been suggested to limit the extension (to 50%) to limit the danger. Streth tests were performed (upper left photo). to examine the difference between a limited bungee cord and one without limits. The bungees were stretched and the force-distance data ploted (upper right figure) The area under each curve is the stored potential energy. This is converted to kinetic energy (KE). From the KE the hook velocity can be calculated. The unlimited bungee generated a maximum hook velocity of 100mph. The maximum hook velocity for the limited bungee is 70mph. Both bungees can still be dangerous.

It appears that the limited bungee was made more robust to increase the holding force for 50% elongation. This has a negative effect on this cord's safe use.