In Bangladesh, a simple change in how bricks are fired cleaned the air and saved fuel. It did not make life better for the people who make the bricks. That split result comes from two linked randomized trials, and it is the point of the story.
Researchers worked across hundreds of zigzag kilns to test low-cost operational fixes. Pollution fell and profits rose. A companion study of 246 kilns and 1,442 workers in the Khulna Division then asked who shared in those gains. In the short term, workers saw no gains in pay, safety, health, or freedom.
Why brick kilns matter so much in Bangladesh
Bangladesh is the fourth largest brick producer in the world. About 8,000 traditional kilns supply more than 90 percent of the bricks used at home, fed by rapid urban growth and infrastructure building.
Most of those bricks are fired in coal-burning zigzag kilns. They release carbon dioxide and fine particulate matter, known as PM2.5. That fine fraction matters because it can enter lungs and blood, with PM2.5 exposure linked to years of lost life expectancy across South Asian cities, and ambient air pollution remains a large public health burden in South Asia. Sector estimates attribute roughly 17 percent of the country’s CO2 emissions and 11 percent of particulate matter pollution to brick manufacturing, with about 6,000 premature adult deaths each year linked to kiln pollution.
Moving kilns away from people sounds simple. It is not practical in one of the most densely populated countries in the world. Schools, clinics, and neighborhoods sit close to kiln fields, so the team led by Nina Brooks at the University of Michigan, Grant Miller at Stanford University, and technical lead Sameer Maithel asked a different question. Could existing kilns run cleaner without expensive new equipment?
The low-cost fixes that cleaned up the firing
The intervention did not replace kilns. It changed how workers fire and stack them, with training and technical support through the season.
Think of a zigzag kiln as a long, looping oven where bricks are stacked in channels and heat is pulled through in a zigzag path. In many kilns, coal was thrown in unevenly in large batches, which creates hot and cold spots, incomplete burning, and wasted heat.
- Single fireman continuous feeding: smaller amounts of coal added steadily, so combustion stays even and less fuel escapes as smoke.
- Improved stacking: bricks spaced so air and heat move through the channels, which bakes bricks more uniformly.
- Less heat loss: a thicker ash layer on the kiln top and a cavity wall to close the gate, plus careful use of powdered biomass alongside coal.
No major capital purchase was required. The practices were taught on-site to owners, managers, and workers, and they were designed to pay for themselves through lower fuel use and better bricks. That financial logic helps explain why adoption persisted into the next firing season and even increased.
What changed, measured in fuel, smoke and brick quality
The main field experiment assigned 276 zigzag kilns to a control group or to intervention arms that received the technical package: 89 kilns received the technical change alone, 95 also received suggestions on improving conditions or pay, and 92 served as a comparison. About 65 percent of intervention kilns adopted the recommended firing and stacking practices.
Across all kilns assigned to the intervention, energy use fell by about 10.5 percent. Estimated carbon dioxide emissions fell by 171 metric tons per kiln over a firing season, while PM2.5 fell by about 0.45 metric tons per kiln. Fuel spending fell, and the share of high-quality bricks rose, which lifts revenue because better bricks command a higher price.
The effects were larger among kilns that adopted the practices because of the program. In that group, energy use fell by about 23 percent, while carbon dioxide and PM2.5 fell by roughly 20 percent. The full results are reported in a low-cost intervention that improved combustion and reduced heat loss in zigzag kilns.
| Outcome | What improved | What did not improve in the short term |
|---|---|---|
| Energy and fuel | Energy use down 10.5 percent across treated kilns, 23 percent among adopters; fuel costs down 9.6 percent | No measured gain for workers from fuel savings |
| Emissions | CO2 down 171 tons per kiln per season; PM2.5 down 0.45 tons; about 20 percent lower among adopters | No measured fall in respiratory symptoms, injuries, anxiety, or depression |
| Brick quality and revenue | Quality-adjusted output up; share of top-grade bricks up 8.1 percent | No rise in weekly wages, bonuses or contract coverage |
| Labor conditions | None found as a result of productivity alone | No fall in trafficking indicators, trafficking prevalence or child labor; no rise in protective equipment or amenities |
Valued with a social cost of carbon of 185 US dollars per metric ton, the authors estimate social benefits outweighed costs by about 65 to 1. The point is direct. Cleaner air here did not require owners to lose money. It helped them save it.
Who does the work inside these kilns
Brickmaking in Bangladesh relies on a large, mostly informal and seasonal workforce. Many workers are recruited from nearby villages through labor intermediaries known as sardars, who also supervise on site. About half of workers in the study came from within 10 km and more than two thirds from within 50 km.
Advance payments at recruitment are common. Once the season starts, debt, withheld pay, long days of 12 to 16 hours, and limits on movement can make it hard to leave or bargain. Jobs include molding green bricks from clay, loading them into the kiln, unloading fired bricks, and feeding coal as firemen.
Private interviews late in the 2022 to 2023 season documented how stark baseline conditions were. Using a conservative coding of the trafficking indicator tool, 70 percent of workers reported lacking personal protective equipment, and 71 percent said they had no formal labor contract. About 42 percent reported limited freedom of movement or communication, while 5 percent reported no freedom of movement or communication at all.
That lack of gear has plain consequences. Without masks, goggles, gloves, and footwear, workers face burns, head injuries, eye irritation, and smoke inhalation. The link between smoke and lungs is familiar across the region, from kilns to open burning, including how tiny particles from burning waste shape smog in South Asian cities. For kiln workers, exposure is not distant. It is the workplace.
A second study asked whether workers gained anything
The companion study kept the same technical change but added a labor lens. It followed 246 kilns in six districts of Khulna Division, with private surveys of 1,442 people, usually five workers plus one sardar per kiln. The team measured trafficking with 39 indicators across seven domains, based on criteria from the United States Department of State Office to Monitor and Combat Trafficking in Persons, covering recruitment, contracts, control over daily life, degrading conditions, movement, debt, and violence.
Across all surveyed workers, the trafficking rate was roughly 20 percent, or about 1.1 workers per kiln out of six interviewed. At 49.6 percent of kilns, at least one worker in six met the definition of labor trafficking. Adult workers reported child labor at more than 70 percent of kilns, mostly involving children ages 14 to 17 in hazardous jobs. About 20 percent of kilns had reports of children under 14 working, at a prevalence of about 5 percent.
Against that baseline, the productivity change was real, yet the researchers found no corresponding short-term improvement in trafficking indicators, trafficking prevalence, child labor, wages, or health. Estimates for amenities such as housing, water, toilets, rest shelter, bonuses, and extra meals were close to zero in both the technical arm and the arm that also gave owners information on positive incentives.
The detailed findings are reported in a randomized trial of productivity gains and work conditions in coercive labor markets. The authors stress the time frame. This is evidence about one season, not about what might happen over years if labor markets or outside options change.
Why cleaner air did not mean an easier day
The two results are not a contradiction. They describe two different paths. The first path runs from firebox to chimney. Steadier coal feed and better airflow improve combustion, so less fuel makes the same heat and less smoke leaves the stack. The second path would have to run from profit to people, through higher pay, gear, rest, water, and freedom to leave. That path did not open on its own.
In competitive labor markets, standard theory expects productivity gains to lift wages or conditions over time as firms compete for workers. In coercive settings, that link weakens. When debt, advance payments, and credible threats limit mobility, firms can capture most of the new surplus. The study was precise enough to rule out reductions of 16 to 17 percent in trafficking indicator counts, so the null result is not only about small samples.
Grant Miller put the implication plainly: “Our study shows that we cannot rely on productivity gains alone to do that, at least not in the short run.” Brooks added that the financial case explains persistence: “Because the changes are economically beneficial for owners, they had a strong incentive to continue following them.” Both quotes sit inside the same lesson. A practice can stick because it pays and still leave workers where they started.
There was also a wrinkle about scale. When the team extended work to districts around Dhaka, adoption was lower than in Khulna, yet kilns that did adopt saw similar fuel and emissions benefits. Owners cited thin margins, volatile coal prices, uncertain demand, and shifting regulation. A change that pays on average can still feel risky when cash is tight and conditions vary by kiln size, land, and local practice. The scale-up effort has since trained more than 1,000 kilns across the two divisions, and key elements of the training were formally included in the Bangladesh National Air Quality Management Plan 2024 to 2030.
What would have to change for gains to reach workers
The research team is now testing measures aimed directly at workers, developed with piloting and conversations at kilns. They include masks for coal crushing, goggles and footwear for firemen, head protection for carriers, plus sanitation and cooking facilities, shaded rest areas, clean water, heat stress information, and information about child labor. Field staff expected pushback, but many owners described the cost as negligible next to running a kiln and said better-supported workers do better work.
That response matters because it separates two tasks. Cleaning combustion is largely a technical and training task with a built-in reward. Improving daily life is a management and accountability task. It needs its own design, its own follow-up, and its own way to verify change, rather than assuming profit will do the work.
Readers who live with smog often notice effects before they see data, from irritated eyes to lingering congestion, a pattern described in how repeated exposure to air pollution can accumulate in the lungs. For kiln neighbours, lower PM2.5 is still good news. For kiln workers, the air inside and around the kiln is only one part of the bargain. Contracts, debt, movement, gear, and hours decide the rest.
Frequently Asked Questions
What kind of pollution do brick kilns produce?
Coal fired zigzag kilns release carbon dioxide, which warms the climate, and fine particulate matter or PM2.5, which harms health. Uneven firing and heat loss raise both fuel use and smoke. The intervention cut energy use and both pollutants by improving combustion and keeping heat in the kiln.
Why not simply move kilns away from people?
Bangladesh is densely settled, and kilns number in the thousands near towns, schools, and health facilities. Relocation at that scale is not feasible, which is why the team focused on making existing kilns cleaner where they stand.
Did wages or worker health improve after kilns became more productive?
No, not in the study season. Weekly wages, respiratory symptoms, workplace injuries, and validated anxiety and depression scores showed no significant decline or gain from the productivity intervention. The authors describe this as a short-term finding, not a prediction about all future effects.
How did researchers measure trafficking and child labor?
Workers were interviewed in private with a 39 indicator tool covering recruitment, contracts, control, living conditions, movement, debt, and violence. A worker counted as trafficked if indicator combinations met thresholds set by trafficking prevalence guidance. Child labor was reported by adult workers by age group and team, with all kiln jobs treated as hazardous given the near-total lack of protective equipment. Children were not interviewed directly.
What happens next for workers?
The team returned in a later season with worker-focused recommendations on gear, water, sanitation, rest, heat, and child labor information. Early field reports found many owners open to low-cost steps. Whether those steps change measured trafficking, child labor, pay, and health is the next test, and it will need the same careful tracking as the emissions result.
What this pair of studies leaves us with
The kiln fix worked. Less coal, less smoke, better bricks, and lower costs. The labor result qualifies the celebration without erasing it. In kilns where coercion limits bargaining power, productivity alone did not improve conditions in the short run.
That is a hard but useful line to hold. Clean production and fair work are separate goals. One can be advanced with airflow and ash layers. The other will take direct attention to contracts, debt, safety, and voice, measured worker by worker.
