Human Fall Flat

This achievement is located in the second are of the game (looks like a kitchen). Follow the progress of the mission and turn on the vacuum cleaner (unmissable). After you turn on the cleaner, jump down and grab the nozzle. On the ground you will find three piles of ash. Suck up these 3 piles with the vacuum cleaner nozzle and the achievement unlocks (probably time-delayed again)

In case you need a visual guide, here is my 100% walkthrough of this mission (no voiceover)
05:10 - Spotless clean

Top Shelf: 2:10
Spotless Clean: 4:45
Floor is Lava: 12:50

Miniature Level Walkthrough:

This achievement can be earnt in the kitchen area of the Miniature level. Once you've dropped down the drain pipe into the kitchen. Take your first right into the open cupboard. Grab the bottom of the hanging spatula and drag it up the stack of boxes, the intention is to use the spatula as a ramp to enter the green hatch above you. Once you've pulled yourself up to the worktop, bear right, jump and swing on the metal tongs to land on a baking tray. From here jump to the next baking tray. You should then be able to see an open draw which you can drop into. Drop inside and climb the wooden logs to exit through the hatch above. Here you should be able to jump onto the top of the hover, switch it on by pulling the red switch down. With the hover now running you can safely drop to the floor, grab the nozzle and suck up the three piles of ash on the floor. Once all three have been cleaned up the achievement should pop.