Are there any guidelines associated with the position of the collection head when doing personal dust monitoring and the person being monitored is wearing a positive pressure hood?

We believe the collection head should be external to the hood (potential exposure) not inside (actual exposure). Is this correct?

The HSE publish MDHS leaflets. 14/3 is on dust sampling. Paragraph 27 says "In personal sampling, the sampler is attached to the wearer within his or her breathing zone, and the pump (if external to the sampler) is connected to it by a length of flexible tubing and worn on a belt, harness, or in a pocket. The breathing zone is the space around the worker's face from where the breath is taken, and is generally accepted to extend no more than 30 cm from the mouth. Personal sampling instruments are normally mounted therefore on the upper chest, close to the collar-bone."
As to the second part of the question it depends on what you are measuring. If you want to know the dust in the air around the worker then outside the mask. If you want to measure the efficiency of the RPE then inside the mask