This article is about a/an term in Kamen Rider Build.
Hazard Level (ハザードレベル Hazādo Reberu) is a term coined by Faust to measure a human's resistance to Nebula Gas. A low Hazard Level means that a certain individual would have a much lesser chance of withstanding the gas' effects and have greater chances of dying. Higher Hazard Levels would allow a certain individuals to perform feats that would normally require a prerequisite Hazard Level. Raising one's Hazard Level also seems to nullify psychological effects of the Pandora Box and Nebula Gas, such as Sento Kiryu being able to use the Hazard Trigger for longer periods of time without going berserk and Gentoku Himuro's paranoid and cruel personality traits gained during the Sky Wall Disaster disappearing after being experimented on by Namba Heavy Industries.


Individuals with Hazard Level 1 would die a short while after being administered with the gas, while individuals with Hazard Level 2 would immediately be converted into a Smash. Anyone with a Hazard Level above Level 2 would retain their human form even after being administered with the gas, with prime examples being Sento Kiryu and Ryuga Banjo. According to Gentoku and Takumi Katsuragi's data, anyone with a Hazard Level above Level 3 would be able to use the Transteam Gun or Build Driver, while those above Level 4 are able to use a Sclash Driver.Night Rogue Chapter However, while a Level 5 Hazard Level is required to use the Evol-Driver, it's assumed that no Human originating purely from Earth is capable of naturally reaching that Level. The Final Weapon: Evol

Evidently, Faust's experiments were to isolate people with Hazard Levels high enough to use the Rider System so they could create an army of Kamen Riders for military purposes.

Theoretically, the Hazard Level of humans may be raised through two means: temporarily through strong emotions, and permanently through the continual usage of purified Fullbottles and the Rider Systems.


Hazard Level of Riders

Blood Stalk reading Hazard Levels

The first Hazard Level mentioned in the series was Kasumi Ogura's. Due to her unnamed illness, her physical state could not withstand the transformation of being turned into a Smash. Night Rogue labeled her as "Hazard Level 1", claiming that once anyone extracted her Smash Essence, she would die immediately. Ryuga bitterly allowed Sento to extract her Smash essence, thus killing her. Her Smash essence was later purified into the Dragon FullBottle, which Ryuga treasured greatly. The Innocent Runaway

Sento Kiryu/Kamen Rider Build is given Hazard Level 3.2 and later 3.7 by Blood Stalk, who notes that anger leads to his Hazard Level increasing. Dangerous Identity

While fighting Ryuga, Blood Stalk calls him Hazard Level 2.4, which grows incrementally to 2.7 throughout the fight. Memory Starts To Talk Later, due to Ryuga's determination and strong synchronization with the Dragon Fullbottle, his Hazard Level rose to 3.0 Technology of Destruction, thus allowing him to become Kamen Rider Cross-Z. Burning Dragon

By fighting as Kamen Rider Cross-Z, Banjo was able to push his Hazard Level to 4.0, allowing him to use the Sclash Driver.

Ryuga's Hazard Level later reaches Hazard Level 5 due to his alien physiology, thus allowing Evolto to possess him and use the Evol-Driver.

Known Levels

Level Description
1 Subjects will die upon exposure, and ultimately when defeated as a Smash; normally caused by a pre-existing illness.
2 Subjects will transform into a Smash, but regain their humanity upon defeat, albeit with short-term memory loss. The most common Hazard Level.
2.1+ Subjects retain their human forms after being dosed, seemingly suffering no side effects.
2.4 Ryuga Banjo at the start of his fight with Blood Stalk.
2.7 The peak of Ryuga's Level at the end of his fight with Blood Stalk.
3 The minimum Hazard Level required to use the Build Driver. Eventually reached by Ryuga.
3.2 Sento Kiryu during his first fight with Blood Stalk.
3.6 Kiba's Hazard Level in his Hard Smash form, as measured by Blood Stalk. The Forbidden Item
3.7 Sento's Level when angered. Also the Hazard Level of Akaba and Aoba in their Hard Smash forms. The Forbidden Item
3.9 Sento's Hazard Level when using Rabbit Tank Sparkling, as measured by Blood Stalk. The Forbidden Item
3+ Nariaki Utsumi's initial Hazard Level, as evidenced by his usage of the Transteam Gun.
4 The minimum Hazard Level required to use the Sclash Driver. Ryuga's Hazard level when using the Sclash Driver The Forbidden Item
4.2 Kazumi Sawatari's latest Hazard Level, as measured by Blood Stalk. The Forbidden Item
Sento's Level before quickly increasing to 4.4. A Man Called Rogue
4.4 Sento Kiryu's Hazard Level while in Hazard Form, as measured by Blood Stalk. A Man Called Rogue

Gentoku Himuro’s Hazard Level, as evidenced by his usage of the Sclash Driver.

5 The Hazard Level necessary to use the Evol-Driver. According to Shinobu Katsuragi's research, it is impossible for a normal human being to reach this level. The first person to reach this level was Soichi Isurugi/Evolto. Ryuga was eventually able to reach this level as Cross-Z Magma at the end of his fight with Evolt.
6 Sento's Hazard Level after using a Pandora Box panel in the Build Driver. Evolto Hunts the Stars
6.3+ Sento's Hazard Level after raising it by cranking the Build Driver's Vortex Lever with the Pandora Box panel inserted.
7 Ryuga's Hazard Level after remembering the destruction of Mars when he was part of Evolto. This Hazard Level was soon reached by Sento as well. Achieving this Hazard Level has a physical effect on Fullbottles, changing Dragon and Rabbit into Silver Dragon and Gold Rabbit, respectively. 


  • Hazard Level might refer to the real-life biological hazard and biosafety level.
  • The systems which adhere to a given Hazard Level are generally graded by both the users' adaptibility/compatibility for each form and the Hazard Level itself. This implies that it is not the quality of the transformation that defines a Rider's power, but simply their combat proficiency, affinity with the transformation items, and Hazard Level. This has been shown with Shinobu Katsuragi using basic Best Match forms, yet dominating the other Riders, despite two of them having Sclash Drivers, and one user possessing a Hazard Level that was initially believed impossible for humans to achieve. Another Build
    • Past instances where power is more dependent on the Rider than the system has been seen in the Armored Riders from Kamen Rider Gaim, with elements taken from other series like Kamen Rider Blade's Fusion Co-efficiency and Kamen Rider Wizard's Mana.
      • A parallel to the two elements is when one or the other becomes to much to control, the resulting reaction becomes irreversible. However, this results in death, as opposed to a manifestation of the power taking over like Mana, or a mutation like the Fusion Co-efficiency.
Sento Kiryu - Ryuga Banjo - Kazumi Sawatari - Gentoku Himuro - Evolto - Nariaki Utsumi - Shinobu Katsuragi - Kengo Ino - Killbas
Transformation Gear
Fullbottles - Build Driver - Transteam Gun - (Great) Cross-Z Dragon - Sclashjellies - Sclash Driver - Hazard Trigger - Nebulasteam Gun - Cross-Z Magma Knuckle - Evol-Driver - Evol-Trigger - Grease Blizzard Knuckle
Drill Crusher - Hawk Gatlinger - 4Koma Ninpoutou - Kaizoku Hassyar - Fullbottle Buster - Steam Blade - Beat Closer - Twin Breaker - Muscle Glove - Solstall Wings - Giant Scratcher - Space Ride Arm - Spine Knuckle - Long Range Cleaner - Trash Converter - Gold Lio Gauntlet - Multi Deluge Gun
Pandora Box - Halfbodies - Fullbottle Holder - Build Phone
Hazard Level - Project Build - Sky Wall - Nebula Gas
nascita: Misora Isurugi - Soichi Isurugi - Sawa Takigawa - Kazumi Sawatari - Gentoku Himuro
Prime Ministers: Taizan Himuro (Touto) - Yoshiko Tajimi (Hokuto) - Masakuni Mido (Seito)
Namba Heavy Industries Ltd.: Juzaburo Namba - Nariaki Utsumi - Guardian
Hell Bro's: Fu Washio - Rai Washio
Aliens: Vernage - Evolto
Gentoku Himuro - Evolto - Nariaki Utsumi - Takumi Katsuragi - Shingo Kuwata - Eita Kawai
Touto: Needle Smash - Strong Smash - Burn Smash - Flying Smash - Mirage Smash - Square Smash - Press Smash - Ice Smash - Stretch Smash
Hokuto: Castle Hard Smash - Stag Hard Smash - Owl Hard Smash
Kaiser: Kaisei Mogami (World of Ex-Aid)
Kengo Ino - Ryoka Saiga - Mitsuomi Gohara - Evolto - Killbas