Poor edge quality there are many potential causes for spontaneous breakage of tempered glass.
Safety sliding glass door shattered.
Although tempered glass in general is stronger than non tempered glass especially when it comes to direct impacts to the face of the glass it can still break.
Safety glazings are commonly required for sliding glass doors shower doors and patio furniture.
By design tempered glass completely shatters into thousands of small pieces when stressed beyond its capacity and serves as a safety feature which helps avoid more serious injuries from the larger sharper shards often seen in the non tempered glass.
I think we have the details for the contractor that installed the doors 15 years ago and will give them a call to discuss repairs.
Spontaneous breakage is a relatively well known in the glass industry but somewhat rare phenomenon associated with tempered safety glass.
One rather common cause of tempered spontaneous breakage is known as a nickel sulfide inclusion.
Since tempered glass is twice as strong as ordinary glass patio doors are not broken as easily as they once were.
However patio glass doors are not invincible and can shatter in high winds or if they are struck with a hard object.
The glass is designed with safety in mind.
Recently manufacturers of patio and sliding glass doors started using tempered glass in their products.
Safety glazing generally refers to any type of glass that is engineered to reduce the potential for serious injury.