I'm not referring to normal venting. Unless there's a sudden loss of pressure in the cargo hold.
The depressurization relief vents are incase of a sudden loss of pressure as happened with 2 Boeing DC-10, American Airlines Flight 96 and Turkish Airlines Flight 981.
Source for information below American Airlines Flight 96
The cabin floor failure was also a matter of poor design. All of the other portions of the cargo holds had holes cut into the cabin floor above the cargo areas. In the case of a pressure loss on either side of the floor, the air would flow through the vents and equalize the pressure, thereby eliminating any force on the floor.Only the rearmost portion of the cabin lacked these holes, and it was that portion that failed. Because the control cables were running through the floor for the entire length of the aircraft, however, a failure at any point on the floor would cut controls to the tail section.">
Source for information below Turkish Airlines Flight 981.
Finally, although there was apparent redundancy of the flight control systems, the fact that the pressure relief vents between the cargo compartment and the passenger cabin were inadequate and that all the flight control cables were routed beneath the floor placed the aircraft in grave danger in the case of any sudden depressurization causing substantial damage to that part of the structure.
That is normal as well depending on the aircraft.