I don't suppose they have an on-site supply of rebated diesel ? ;-)

Like John M, I would go for the softly softly approach here Daisy (not the normal Zimmy way I grant you). Just point out the re-fueling is not a good plan (Need an RA for that as you know) and that Diesel fumes cause cancer and ... well you know the rest. But don't whatever you do 'let it go in hard as per zimmy style' :-) They will like you and respect you more.

Daisy maisy Is there enough room outside the warehouse for the contractors to park if so I would suggest that they can take there vehicles in first thing in the morning to unload but then remove them to a area outside the warehouse. thus reducing fumes and the risk of people coming into contact with and vehicles plant as there is ever only one winner when this happens , if they still insist I would suggest a segregated fenced off parking area with a current site traffic management plan detailing segregated pedestrian walk areas , hope this helps just one last thought are they using the vehicles at break time, is there adequate welfare providedon site to prevent them using their vehicles Chris

I'm with the rest of the gang when it comes to how this should be handled. There's times where you will need to dive in and 'stop the job' but not many, and definitely not in this case. Regardless of your experience you need to have the confidence to ask some simple questions when on site. What you see may (and it is may) have already been considered but you'll only know for sure when you ask. If they've not given it consideration then ask if they're aware of the risks and ask how they would manage them to prevent an accident or exposure to something that can cause ill health. Given the size of the warehouse and from what you've posted I'd suggest that the one thing that doesn't sit right is the fuel. You need to ask what the fuel is being used for and from the answer consider if some action should be taken to mitgate spills and deal with fire. The fact that a funnel was present could be considered a good thing as they're not sloshing fuel around when filling. Always remember that a quiet word goes a long way and bear in mind that we help manage and understand risk for our employers. Also remember that you're a representative of your employer and in a position where you should be able to manage certain situations without raising to a higher level. Always let them know what you've found but be sure to demonstrate you can manage a situation there and then whilst still letting the job get done (albeit safely). With that in mind go back to basics, identify the hazards, assess the likelihood and severity and then reasonably look at what should be done. Discuss with the staff on site and discuss with the contractor management, then agree a reasoned course of action.

I know I should of spell checked warehouse spelt wrong twice

Daisy Provided the vehicle engines aren't left running or being driven around inside the warehouse other than to park them initially I would consider this relatively normal for a project like this.