Hi, I am planning to arrange that our building surveying team access some redundant plant and equipment including dryers, combustion chambers, extractors, sulphuric acid and sodium silicate chambers. I am to find out if there is and residual content of hazardous substances and as to whether they are needing to purge the confined spaces in advance. My main concern is the confined spaces so the query relates to whether it is necessary for us to wear full positive pressure breathing apparatus once the area has been purged?? Is there any chance of further hazardous fumes ingressing or generating from residues once the purge has been conducted, or does it remain to be prurged whilst we are accessing such??

You need to look at the ACOP and there is much more to entering a confine space than using a gas monitor. The starting point is a detailed risk assessment and method statement. The need to wear breathing apparatus is dependent on the risk. Breathing apparatus is either needed because you know there are toxic gases or they are highly likely to be present and possibly for self-rescue.

You can get gas monitors that you can fit suction tubes to that allow you to test a confined space without entering it. If you are unsure or believe you are not competent enough to organise it contact a specialist like Mines Rescue, expensive but good.

Please also consider if relevant persons disturbing gas trapped in sediments or sludge. I have had clear air monitoring results on entry, that suddenly start to register gases released by persons "walking on crud" and releasing trapped gases.

Birchall

you also need to consider the substances (potential) contained within the confined space and atmosphere before deciding on the correct method of purging; airing, steam, nitrogen followed by air, water etc.
A gas/air test will be necessary following purging and before entry, however as above you need to understand what substances/gases you are measuring for.

Without detailed certification of cleaning you should not really expect to be sending anyone into this sort of area. BS are also the last people I would expect to be competent in the use of Positive Pressure PPE and protective wear. Get the experts in to clean and flush properly and undertake surveys. Plant will need cleaning properly before dismantling in any case.