Haz area 150m head submersible

[UKAndy]

I am looking for a submersible pump for use in a hazardous area (oil and gas). It needs to fit down a 12" caisson and pump oily water to a head of 150m. The idea is to empty the caisson for inspection. An air driven centrifugal submersible would be ideal but I dont know if one exists for this duty. The flow rate is not critical, as there is no definite time limit to pump out the caisson. Any suggestions?

Is there a better way, would a jet pump work (we have a high pressure water supply), can I submerge a diaphram pump if I plumb the exhaust to surface.

regards,

Andy