Safety is a key concern when it comes to mining. Big Pit is still classed as a working colliery in the eyes of the law, and the strict 'Mines and Quarries Act' applies even thoughvisitors, not coal, are the main business of the mine today.
Look left into the Pit Top area. You may see the white bullet-shaped cage in the picture, which is known as the 'kibble'. This is part of the equiptment necessary for an underground rescue, should it ever be needed.