Wooden Platform Bonding

Is there a chance of step voltage?

You need to do a risk basement based on local conditions. Conditions we know nothing about.

What did yout electrical safety department/responsable said about that?

Is the wood going to become live, then? How strange.

Seems strange. Is this a permanent situation or temporary for maintenance/commissioning?

I take it this is outside in some sort of large factory switchyard (or possibly a substation)?

How big/high is the cabinet?

What country is this in, what standards are you working to?

Why not an all metal structure properly bonded back to earth as would be common for outdoor access structures in switch yards or substations? What do your local standards say regarding structures in this situation?

This is a Darwin Award in the making.

First you want to work on an energized high voltage circuit breaker,

Second you want to build an elevated wooden platform that will potentially reduce the clearance between the bottom of the energized bushings and your personnel,

Third you want to eliminate the insulating properties of the wood and ensure a really good path to ground for your personnel by making them stand on a grounded metal grid instead of the isolation provided by the wood/crushed stone, and

Forth you're ignoring the fact that Anonymous strangers on the web may not be any more qualified to give advice than you are to implement it, and certainly have no culpability when things go wrong.

Hire a firm that specializes in live equipment maintenance, at a minimum you may prevent a blackout if someone's tool slips or they jumper the wrong contacts, and in the best case you may save someone's life.

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Usual practice is an earth mat under the switchyard floor to prevent step voltage. If ever you've see cattle killed by simply approaching a fault the reason becomes obvious. When approaching a switch I was taught to do the shuffle, never place one foot fully in front of the other.
Rather than a wooded platform metal would be preferable.

A dead tank breaker isn't going to have HV in the cubical or anywhere near ground level. You'll probably find a load of mechanical/hydraulic/pneumatic stuff.

The National Electric Safety Code (not to be confused with the NEC) allows the use of safety mats as supplemental protection around live equipment:

Section 124.C.4 Mats...may be used at switchboards, switches, or rotating machinery as supplementary protection.

The clearances to live parts needs to be maintained especially if work is being done on a raised platform:

The distances depend upon a table that considers the phase to phase voltage and the BIL of the system, neither of which has been stated. I've been in 500kV switchyards when switching transients caused flashovers between arcing horns so I'm a bit respectful of the vagaries of high voltages. Distance keeps you alive.