Coytanger You fail to mention how you are going reach the chimney stackes IE stage scaffolding, MEWP, cat ladder ?

Are you likely to drop anything bigger that a scaffold component- i.e. ask you're scaffolding erector what his standards are? Is the work likely to involve 'ejection' of items such that there is a significant horizontal component on the trajectory? Beware sheets, boards and other "sails" or lightweight components which can become wind-borne and bear in mind the WAHR requirement to prevent falls (including falling objects) in the first instance.