This can be traced back due to a lack of maintenance. Both broken and damaged slat clips move across, and into the drive chain. This ultimately causes slat end damage. In the worst cases, the drive chain can be forced off the drum sprocket and the curtain will then rapidly descend with out the chain that is connected to hold the drum.
The curtain grabbed on the top of the side guide and the whole curtain unrolled on a 45 degree angle.
Drum spring failure is another common maintenance issue. Roller shutters are spring balanced, meaning the drive unit assists lifting the door. A torsion spring inside the drum is calculated in size to provide force that lifts approximately 80% of the doors weight. As you can imagine once the spring snaps or fatigues, the motor does all the work. This reduces the drive units life span and caused premature failure. The broken sharp end of the hardened spring causes damage to the comparatively soft mild steel drum casing. In extreme cases of neglect, the sharp spring will neatly cut the drum casing in half, causing a catastrophic failure. The two doors below look okay, don’t they? Well, unfortunately, they both have broken drum springs. Luckily tenants in the building complained about a squealing noise.