One of the first things to look at is modifying the existing switchgear to reduce the likelihood of a flashover occuring.
It may be possible to add insulation to busbars and joints to prevent direct contact. Great care should be taken when doing this to ensure that the insulation added does not create partial discharge within the switchgear.
It may be possible to fit segregation boards between conductors to prevent shorts occuring between them.
If the spout shutters are made of metal, it may be possible to have insulted shutters made to replace them or to attach a layer of insulation around the existing shutters.
If the switchgear design allows it, you could also look at fitting bursting discs to reduce pressure build up from an arc and direct hot debris and fumes away from where operators stand in front of the switchgear.