However, the rear door tanks are almost always empty when the BMP goes into combat, as they are only meant to increase the road travel range of the vehicle. In intense war areas where the BMP sees action often, and it is relatively near to its base of operations, instructions highly recommend detaching the rear door tanks from the fuel system, filling them with sand as additional protection for the troop compartment, and adding fuel to the internal main fuel tank from other sources when the need arises. This was not practiced by some BMP-1s crews during a number of local conflicts, e.g., in Chechnya, which resulted in frequent attempts by the enemy to hit the rear doors of the BMP-1s. The inner fuel tank is more vulnerable than that of many modern IFVs – the thin side armor means that penetration is likely to occur to the inner fuel tank as well. Another potential flaw in the BMP-1 is its troop seating layout. In order to allow the infantrymen to use their assault rifles and machine guns while on the move, firing ports were installed in the sides of the hull and in the left rear door. Soldiers are seated on two back-to-back benches, mounted along the center line of the troop compartment. If hit by a more advanced type of magnetic anti-tank mine, the resulting explosion could kill the entire complement of infantrymen. In many other troop carriers, soldiers are seated on separate benches against the hull sides. This layout might prohibit the use of infantry weapons from inside the troop compartment, but in most cases the loss of life from a mine would be significantly less, although the loss of lower limbs would still be frequent. It should also be noted that most conscript soldiers do not receive much training in firing from inside the vehicle while it's moving. Even for professional soldiers, the unstabilized firing port periscopes makes it very difficult to conduct aimed fire while on the move. Nevertheless, the ability of soldiers to use their weapons from inside the vehicle is of extreme importance during urban warfare, especially, when repulsing enemy ambushes. The BMP-1 has no air conditioning or air cooling system, its crew members and passengers suffer heavily in hot climates as its air filtration system and exhaust-ventilation fans cannot provide any comfort at high temperatures. During the Yom Kippur War, crews kept some of the roof hatches open. This meant that they were vulnerable to machine gun fire from higher ground. Only a few examples of the BMP-1 were intended for export – mainly to countries with a hot climate (for example, the Slovak-Belorussian "Cobra-S"), they are equipped with an air conditioning system.