Thankyou John,

As Iv previously mentioned I worked for 20y in Castleford,West Yorkshire which was a major centre for chemical manufacturing,there being at least three factories the largest called Hickson's.
There are archive photos of toxic foam blowing down the streets from the river,a situation which was classed as an emergency and the town was put on alert.
How would one go about finding the data to identify a cluster ?
Just as an aside I also had a client in Bradford who got cancer. She worked for Ciba in the accounts dept which was situated above the loading bay. When she went for treatment the oncologist said "not Ciba again"
The lad who shared a desk with her was diagnosed with early onset PD.

As always I greatly appreciate the time you take to produce such detailed and interesting posts for the benefit of all.

Nigel