Companies are coming out with QD covers for muzzle devices.

Griffin Armament has their QD Blast Shield. It slips over their muzzle devices and locks in place.

According to Griffin Armament:

The Griffin QD Blast Shield is compatible with our line of QD 5.56mm mounts, Including the Flash Comp, Muzzle Brake, Compensating Flash Hider, and Tactical Compensator. It is also compatible with A2 Compensators that fall within the NATO spec blueprinted dimensions. Although many companies manufacture A2 style compensators not all of them are dimensioned properly. Not Compatible with BCM, BCE or PWS muzzle devices.

They are best suited for short barreled rifles or pistols like the AR pistol.

The jackets help direct the muzzle blasts to avoid hitting any fellow range users on either side of the shooter.

Gemtech has their version called the Blast Jacket.