Explainer: The chemistry of green crackers work, and how they help

Published on Oct 24, 2022 04:01 PM IST

Green crackers seek to produce the same light-and-sound effect as conventional crackers but emit lower amounts of pollutants. To know what ingredients they use, it is necessary to first understand what goes into a conventional cracker.

A firecracker consists of three main components: a fuel, an oxidiser, and a binder. (Representative Image) PREMIUM
A firecracker consists of three main components: a fuel, an oxidiser, and a binder. (Representative Image)

New Delhi: As in previous years, a number of states have banned pollution-causing firecrackers ahead of Diwali, allowing only those that have come to be known as green crackers. So, what makes a cracker green?

Green crackers seek to produce the same light-and-sound effect as conventional crackers but emit lower amounts of pollutants. To know what ingredients they use, therefore, it is necessary to first understand what goes into a conventional cracker.

Making of a cracker

A firecracker consists of three main components: a fuel, an oxidiser, and a binder. The fuel is typically a carbon-based compound. The oxidiser, which provides the oxygen necessary for the reaction leading to the explosion, is potassium nitrate in many commercial crackers. The binder, which some makers treat as optional, and whose role is to allow for a stable reaction, is often sulphur.

Additionally, metallic components are put in to help create a spectacle. Aluminium powder is a common ingredient, often acting as the fuel itself, which is added to produce bright flashes of white, for example in sparklers (phoojharis). Other metallic additives used around the world include barium salts (which produce green flashes of light), copper compounds (blue), calcium salts (orange), and strontium compounds (red).

Harmful chemicals released into the air as a result of the explosion, besides carbon dioxide, include ozone, sulphur dioxide, nitrogen dioxide, carbon and various hydrocarbons. A number of studies over the years have reported an increase in particulate matter (PM2.5 and PM10) in the days after Diwali or other occasions involving large-scale bursting of crackers.

How green is different

Green crackers have the same pyrotechnic composition (fuel, oxidiser and optional binder) as conventional ones, but generate fewer emissions because of their additional ingredients. “The usage of conventional chemicals like aluminium, metal nitrates and sulphur have been reduced in the green firecrackers by using multifunctional additives,” Dr Sadhana Rayalu, Chief Scientist at National Environmental Engineering Research Institute (NEERI), told HT in an email response.

NEERI, which functions under the Council for Scientific and Industrial Research (CSIR), is leading the effort to develop green crackers in collaboration with other institutes.

The chemicals that replace conventional ones differ from green cracker to green cracker.

* STAR, which matches the sound emitted by commercial crackers, uses ferric oxide as the oxidiser in place of a metal nitrate. Other ingredients include aluminium, sulphur, potassium nitrate (in lower concentrations than in conventional crackers) and NEERI’s proprietary additives. These additives help suppress the chemicals released in the explosion.

* SWAS, another cracker that matches the sound levels of commercial crackers, exploits water released during the process of ignition for two purposes. First, the water itself reacts with some of the ingredients, leading to the generation of heat. Second, the water and some of the fragmented additives suppress the dust released. Besides aluminium and lower quantities of sulphur and potassium nitrate, the ingredients include NEERI’s proprietary additives and calcium peroxide, which releases water, and boric acid, whose reaction with the water leads to the generation of heat.

* SAFAL exploits heat generated by zeolite, an additive. Dry and hydrated zeolite, packed atop the basic ingredients, releases water on heating, which acts in a way similar to the processes that take place in SWAS.

How that helps

The health hazards posed by chemicals released from the bursting of conventional crackers are widely documented, as are the health risks from high PM concentrations in general. Rayalu cited short-term health impacts such as discomfort in breathing and upper respiratory diseases, and long-term impacts such as asthma and bronchitis.

How much green crackers can reduce these hazards will depend, obviously, on how much they can release the release of harmful chemicals. Results of tests posted on NEERI’s website indicate that crackers such as STAR and SAFAL release 30% less particulate matter as compared to conventional crackers.

“New formulations meeting 50-70% emissions reduction target have been developed (stability and sensitivity testing in progress),” Rayalu said.

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  • ABOUT THE AUTHOR

    Puzzles Editor Kabir Firaque is the author of the weekly column Problematics. A journalist for three decades, he also writes about science and mathematics.

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