No other workers remain in the tunnel at this time, according to Mack, and no one was exposed to harmful gases as a result of the accident.

CNN: STORY HIGHLIGHTS

Peat bogs are a natural carbon sink absorbing harmful gases.

BBC: Concerns raised over wind turbines and wild land

One analyst told the BBC the military might ultimately wish to equip soldiers with a range of these pencils to provide a portable test kit for a range of harmful gases.

BBC: MIT pencil 'draws' gas sensors onto paper

Fuel cells offer several advantages: they do not have moving parts and there is no burning involved, so there are negligible emissions of environmentally harmful gases like nitrogen, sulfur oxide and carbon monoxide.

FORBES: Magazine Article

Whatever paths we take toward that goal, whether shifting to renewables and nuclear, or finding ways to keep harmful gases out of the atmosphere once created, the journey will inevitably be costly, requiring massive investments in technology, research and re-engineering the ways in which we live and do business.

FORBES: Without Affordable, Clean Alternatives, South Africa Turns to Coal

At first glance, the pro-environmental rulings handed down by the Supreme Court this week seem to bode unfavorably for utility companies as owners of power plants that produce harmful greenhouse gases such as carbon dioxide.

FORBES: Greener Days Ahead?

Most of these deaths occur in developing countries where larger amounts of harmful chemical compounds such as toxic gases and particulate matter are released in the atmosphere.

UNESCO: 2015 For Women In Science Fellows