The chimneys on the horizon outside a Punjab town belong to Bull's trench kilns, oval brick kilns fired continuously, in which a fire moves around the ring while bricks are loaded on one side and drawn on the other.
Punjab has several thousand of them. They consume soil from the fields around, coal and increasingly whatever else burns, and they are among the largest sources of particulate air pollution in the state.
The workforce is largely migrant and works on advance payment, which in a number of documented cases functions as debt bondage, with whole families including children moulding bricks by hand at piece rates.
Zigzag firing technology, mandated in stages since 2017, cuts emissions substantially and adoption has been partial.
Every concrete house in a Punjab village is made of these bricks, and the labour conditions that produced them are known and not discussed.
A kiln takes the topsoil off a field, usually leased for a term of years, and the field is returned lower and poorer than it was. There is no requirement to restore it.
The advance payment system ties a family to one kiln for a season or longer, and inspection of kilns is minimal.
The kilns are one of the few industries in Punjab where a survey of the workforce has been attempted at all, mostly by unions and academic researchers rather than by the state.