Designing fan bulkhead - is there minimum blast pressure

[ARS97]

We're designing a bulkhead (58' wide x 30' tall) for a large volume, low pressure Howden mine fan. The operating pressure for this fan is less than 1 inch of H20 (5.2 psf). The customer doesn't have any information on blasting pressures unfortunately. Obviously I need to talk with the customer and try to sort this out, but in the meantime, does anyone know if MSHA has a minimum blast pressure requirement? I would think that blast pressure would govern over this minimal fan pressure.

 

[miningman]

I this bulkhead REALLY 58 feet x 30 feet??? That's a big underground excavation!!! Regardless is this a coal or metalliferous mine ?? How close does blasting take place?? Rather than MSHA regs , these will be you defining parameters.

 

[ARS97]

It's an aggregate mine....yeah, it's big. Do you know how they test for the blasting pressure by any chance? I'm trying to convince the customer to spend a little bit of money in order to save some money later. Plus, it takes the guessing out of the equation.

 

[miningman]

OK the good news is since this is not a coal mine , the presence of methane can probably be discounted....... a methane explosion is several orders of magnitude more powerfull than conventional explosives. I cannot give any references to blast pressure but I can safely predict that they would be a function of the amount of explosives and the distance between the blast and the bulkhead.

It might be easier and more effective to focus on the anticipated peak particle velocity at the bulkhead due to any specific blast . This is also a function of the distance betrween the blast and the amount of explosives being detonated instantaneously. The rule of thumb is a PPV of 300 mm / second will crack virgin rock, less than 50 mm/ second is unlikely to crack drywall. ie anything around 100- 150 mm / second should be OK underground. Run the calculations and make sure you are likely to be below 150mm/sec for every blast. If you cant confirm that, then your structure is at risk.

 

[ARS97]

I think I may have talked the customer into performing some blasting pressure tests. They have some data from another nearby mine, where the blasting was taking place much closer to the bulkhead, and the maximum measured pressure was about 13 psf. Thanks for your help on this!