Hydrazine

Hydrazine (ヒドラジン) is an inorganic chemical compound with the chemical formula N2H4. It is a liquid fuel apparently still in use in Academy City for rockets, despite being highly explosive and toxic.

Principles
In Academy City, due to the dangerous nature of the chemical it can only be handled in a limited number of districts such as School District 10, and most likely School District 23 as well. Regardless, it is still used as fuel for rockets. Rockets are constructed in School District 23, and its fuel is loaded there. However, the container portion where the fuel for auxiliary boosters used for altitude control is loaded in School District 10. It is used for Academy City's secret operation of sending out materials into space to build the space port of the Endymion, under the guise of participating in the Venus Probe Contest. It is also used for the rocket that will carry an additional module for the Hikoboshi II.

Toaru Kagaku no Railgun: Uiharu SS
August 1.

1500 kilograms of hydrazine is used as a fuel for the rocket that was to take an additional module for Hikoboshi II into space. However, the vehicle that carried the satellite and 1500 of its fuel has been taken over by a terrorist by threatening that the terrorist would take over the vehicle's automatic evasion system to cause an accident. This forces the driver of the vehicle, Sangaku Youko, to follow the terrorist's instructions. The terrorist's target was a conference between the 12 members of the board of directors that ran Academy City, and the 7 heads of state of other countries in the International Convention Center in School District 3. However, the board of directors have anticipated this, and deemed that it would be far better for the vehicle to crash and incur civilian casualties in order to protect the guests. They hired Sunazara Chimitsu to destroy an overpass in order for the vehicle not to come close.

With combined efforts of Uiharu Kazari, Yomikawa Aiho, Sangaku Youko, and Anti-Skill, the disaster was prevented. Misaka Mikoto and Shirai Kuroko would later go on to capture the perpetrator.

Toaru Majutsu no Index: Road to Endymion
After deducing that Ureapaddy Exica will be using the rockets that are used for the Venus Probe Contest, Touma narrows down the possible ways she could sabotage it, and concludes that since Hydrazine-filled container for the auxiliary boosters are loaded in School District 10 and then transferred to School District 23, she will need to intercept one of the vehicles carrying it for her to sabotage it.

Touma determines the quickest route and discovers her there. She later uses the Brahma Astra to pierce the fuel tank and escape. Index then instructs Stiyl Magnus to use his flame sword to blow the fuel away, instructing him how to modify it for it to be able to remove its toxicity. Stiyl complies and ignites the fuel as Ureapaddy escapes.