How a cracker earns its green label: Inside the lab that tests Diwali smoke

In a sealed chamber at a laboratory in Nagpur, a single cracker is lit. It bursts, it glows, and for a moment, it is just like any other cracker on a Diwali night. But here, the dust it throws into the air is collected, the gases it releases are measured, and its bang is recorded in slices of time shorter than a blink.

This is where a cracker earns its green label. Or fails to.

The test is carried out at the Emission Testing Facility of the CSIR-National Environmental Engineering Research Institute (CSIR-NEERI), the national laboratory that developed India's green crackers. Its firecrackers group is led by Dr R J Krupadam, Chief Scientist and Chair of the institute's Climate Risk, Impact and Adaptation Division.

For Diwali this year, the Supreme Court has allowed only green crackers in Delhi-NCR, and only on November 7 and 8, from 6 am to 7 am and from 8 pm to 10 pm.

So what does it actually take for a cracker to be called green?WHAT MAKES A CRACKER GREEN?

First, a myth worth bursting. A green cracker is not a pollution-free cracker. It is a cracker made from a specially designed chemical recipe or formulation that produces less smoke, dust and harmful gas than a conventional cracker of the same kind.

The bar is set in numbers. A green cracker must release at least 30 per cent less particulate matter, or at least 20 per cent less particulate matter along with 10 per cent fewer gaseous pollutants. Particulate matter simply means the tiny specks of dust and soot that hang in the air after a cracker bursts.WHY CAN'T GREEN CRACKERS USE BARIUM?

Here is the irony at the heart of this Diwali. A green cracker cannot use the very chemical that has made fireworks green for generations.

The colours of fireworks come from metals. When a metal compound is heated in a flame, its atoms absorb energy and release it again as light of a very particular colour. Strontium glows red, sodium yellow, copper blue and barium green.

But barium compounds are toxic, and the Supreme Court has banned them from crackers. So the brilliant green that once lit up Diwali skies is off the shelf, at least in its old form.HOW ARE GREEN CRACKERS TESTED?

To find out whether a recipe meets the bar, NEERI's scientists put it through a trial by fire.

"The emission testing facility is primarily aimed at measuring air pollution, including particulate matter (PM10 and PM2.5) and gaseous pollutants, as well as noise levels," Dr Krupadam told India Today Digital. Cracker smoke carries PM2.5 particles, about 30 times thinner than a human hair, that can travel deep into the lungs. (Representative image: Pexels)

"The firecracker is burst in a controlled chamber, followed by the collection of particulate matter and in-situ sensing of gaseous pollutants," he said.

A controlled chamber is an enclosed space where conditions stay the same for every test, so that one cracker can be fairly compared with another. Nothing escapes into the open air, and nothing from outside disturbs the reading.WHAT IS INSIDE CRACKER SMOKE?

Cracker smoke is not one thing. It is a mixture of solid specks and invisible gases, and scientists measure each separately.

The specks are collected and sorted by size. PM10 are particles smaller than 10 micrometres. PM2.5 are smaller than 2.5 micrometres, about 30 times thinner than a human hair. The smaller the particle, the deeper it can travel into the lungs, which is why these two sizes matter most to health.

The gases, such as sulphur dioxide, which forms when the sulphur in cracker powder burns, are measured in situ. That simply means right there in the chamber, as the cracker releases them, rather than being bottled and analysed later.

The results are then set against those of a conventional cracker of the same type. That comparison decides the verdict.ARE GREEN CRACKERS QUIETER?

Smoke is only half the test. The other half is sound.

A cracker's bang is over almost before the ear can register it, so it needs an instrument fast enough to catch it.

"Noise monitoring is carried out using a Level 1 sound meter to capture impulse noise levels in the microsecond-to-seconds range," Krupadam said. A Level 1 sound meter captures a cracker's bang in spans as short as a millionth of a second. (Representative image: Pexels)

A Level 1 sound meter is the most precise grade of sound-measuring instrument. An impulse noise is a sudden, sharp burst of sound, like a clap or a gunshot. And a microsecond is a millionth of a second. Working across that range, the meter catches both the instant of the explosion and the sound that rolls out after it.

Green does not mean silent. CSIR's own figures put its SWAS crackers at 105 to 110 decibels. On the decibel scale, every rise of 10 sounds roughly twice as loud to the human ear, which makes these crackers far louder than the roar of busy traffic.HOW LONG DOES IT TAKE TO TEST A GREEN CRACKER?

"It takes approximately four hours to test each firecracker sample for air pollution and noise," Krupadam said.

The process is not improvised. "There are standard operating procedures and specially designed equipment for monitoring emissions from firecrackers," he said. This keeps the results consistent from one cracker to the next.

The work has now grown large enough to earn a home of its own. "Currently, I am leading the firecrackers group. Recently, the Director General of CSIR and the Secretary of DSIR established the National Centre of Excellence for Green Firecrackers at CSIR-NEERI to work exclusively on green firecracker research and to support all firecracker-related stakeholders," Dr Krupadam said.

DSIR is the Department of Scientific and Industrial Research, the government department under which CSIR functions.advertisementWHO GIVES CRACKERS THE GREEN LABEL?Once a recipe passes, it is handed to industry. "CSIR-NEERI is a national R&D laboratory that develops low-emission green firecracker formulations and provides them to the Indian fireworks industry through a registration certificate," Krupadam said. R&D stands for research and development.

Only companies that already hold an explosives licence from the Petroleum and Explosives Safety Organisation (PESO) can apply. "Through the online registration system, firecracker manufacturers need to apply with proper documents and a PESO certificate," he said.

The certificate comes with conditions. "It is issued to manufacturers who accept our terms and conditions and strictly follow the quality of chemicals used in the green firecracker formula, as per CSIR-NEERI specifications," Krupadam said.

Without this, he explained, "it is difficult to control the entry of non-green firecrackers into the market. Anybody who knows the formula can prepare firecrackers."

Once issued, the certificate never needs renewing. "The registration certificate is valid for the life of the formulation, and no renewal is needed," he said.

Yet NEERI is clear about what it is, and what it is not. "CSIR-NEERI is not a regulatory agency; it provides green firecracker formulations to manufacturers," Krupadam said. "PESO is the explosives regulator, and it regulates the manufacture, storage, transport and sale of green firecrackers."HOW CAN YOU TELL IF A CRACKER IS GREEN?

Most buyers look for the green logo and the QR code on the box. But the QR code does not come from the laboratory.

"As per the directives of the Supreme Court of India, QR codes or any other similar codes or symbols will be product-specific, and these QR codes are to be developed by the firecracker manufacturers, not CSIR-NEERI," Krupadam said.

Checking what is actually sold in markets is not the laboratory's job either. "Enforcement is by the local administration and PESO," he said.

That leaves a quiet distance between the chamber in Nagpur and the shop counter in your neighbourhood. A cracker is truly green only if its maker follows the tested recipe faithfully, and only if the officials who regulate the market make sure they do.

And even then, green is a relative word. A green cracker still releases smoke, dust and noise, only less of it. In the cold, still air of a north Indian November, that smoke can hang over a city for hours.

The science inside the chamber is precise. The cleanest choice outside it is simple. Light fewer crackers, and let the lamps glow a little longer.- Ends

Radifah Kabir tries to make the universe slightly less mysterious as Senior Sub-Editor at India Today’s Science Desk. A lifelong lover of physics and mathematics, she has spent four years (and counting) translating complex physics papers into English, chasing scientists for interviews, and writing explainers that don’t put readers to sleep. Off-duty, her heart belongs to Lana Del Rey's melodies, Quentin Tarantino's films, poetry, the Star Wars universe, good English movies, series and books, and one very demanding cat.