got-to-get-fit said:
every employer, employing 5 people or more must have a written risk assessment for every task they carry out if it is reasonable that the activity may pose a risk to the individual or others.
Ask to see the risk assessment that has been completed for lone working. this should categorise the level of risk percieved and provide mitigation measures to control or eliminate the risk.....typical measures would include panic alarms, communication devices, lone worker registers and most sensibly not working alone (having a co-worker with you)
If they do not have this risk assessment in place then they are breaking the law under the Health and Safety at work act and also the Management of health and safety and welfare regulations HSG65
.......you do have rights
Indeed they do, but you would be surprised (then again maybe not) by the number of local authorities who do not have risk assessments for this type of work, simply because no-one has done it before and it hasn't cropped up that they need one before.
It is for this reason I would just make a gentle enquiry to see if has been assessed, if it hasn't you are then at liberty to refuse to do the task until an
adequate assessment has been carried out and the identified control measures put in place (just make sure you have union/legal support before you go down that route)
There are a hierarchy of control measures, the first of which would be elimination (i.e. don't do it) the rest is just to mitigate any possible effects of an incident, but possibilities would be mobile 'phones, a dedicated contact centre to register that you have finished work and left site safely etc.
Another question that occurs to me (as Arch says it is a largeish site) is how do people get out if they are locked in after you leave? Can they just jump the fence, in which case what purpose is being served by locking it at night other than it always has been