King Coal by Upton Sinclair

It chanced before many days that Hal got a holiday, relieving the monotony of his labours as stableman: an accidental holiday, not provided for in his bargain with the pit-boss. Something went wrong with the ventilating-course in Number Two, and he began to notice a headache, and heard the men grumbling that their lamps were burning low. Then, as matters began to get serious, orders came to get the mules to the surface.

Which meant an amusing adventure. The delight of Hal's pets at seeing the sunlight was irresistibly comic. They could not be kept from lying down and rolling on their backs in the cinder-strewn street; and when they were corralled in a distant part of the camp where actual grass grew, they abandoned themselves to rapture like a horde of school children at a picnic.