From a young age, we are taught that fire is both dangerous and hot. It is crucial to keep a safe distance from visible fires if we don't have the means to put them out. However, not all fires are visible under normal conditions. For instance, hydrogen burns with a very pale blue flame that is almost undetectable in daylight. This poses a significant problem for organizations like NASA that work with hydrogen.

The Solution for Hydrogen Flames

In 2003, NASA and the Florida Solar Energy Center came up with a remarkable solution - a tape that changes color when exposed to hydrogen. Before this, ultraviolet sensors were used to detect flames, but the previous solution was less effective and less fun. "Given the importance of monitoring liquid hydrogen as it flows through miles of pipeline for every Shuttle launch, where hundreds of thousands of gallons are transferred from a holding tank to the launch pad, this was a crucial development," NASA explained in a blog post.During the Apollo days, detecting hydrogen leaks was done using the "broom" method. Workers would walk around with a broom, stretching the head in front of them. If the broom head started to burn, it indicated a leak. While this method was effective, it may not have been very reassuring to astronauts.

Methanol Fires - A Dangerous Invisibility

In 1981, during the Indianapolis 500 race, racing driver Rick Mears experienced a terrifying incident. Methanol, used as fuel in the vehicles, was accidentally sprayed over his car and the surrounding area, including the pit crew. Some of the methanol caught fire and entered the cockpit, covering his helmet and suit. When he tried to breathe and escape, the flames entered his helmet, burning his nose. "I quit breathing fortunately, but I didn't have a breath because I was struggling to get out, and I kind of kept trying to keep my eyes closed so that it wouldn't burn my eyes," Mears recalled. Several other crew members also caught fire as they couldn't see the flame and approached.

Challenges for Firefighters

Invisible fires pose more challenges to firefighters. Dry chemical powder, carbon dioxide, and alcohol-resistant foam are used to extinguish methanol fires by depriving them of oxygen. Firefighters should wear full-face, self-contained breathing apparatus and impervious clothing, gloves, and boots. For larger fires involving tanks or rail cars, it is necessary to isolate the area for half a mile in all directions and consider evacuating the same distance.The color in regular, visible fires comes from a hot soot of carbon monoxide, elemental carbon, and carbon radicals. It is the soot reacting with oxygen molecules that gives fire its yellow/orange hues, while unburned soot appears as smoke rising above. Invisible fires require special treatment and precautions to ensure the safety of people and property.