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.