Is an old miners cuss word meaning to get Decompression Sickness
or known then as Cassions Disease
When they built the foundations for bridges they worked in water tight containers on the river bed (Cassions) and when they came to the surface too quick bubbles
formed in the body, mostly around the joints causing them to be doubled over in pain. This is known as the Bends
This could last a long time.
Once a worker had this he looked deformed, couldn't work and left a vacancy for a family member/ friend etc. of another worker.