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.


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 Banjou. 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

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

Current 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

Ryuga's Hazard Level later manages to get pushed up to a 4.0, allowing him to use the Sclash 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 Banjou 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+ Soichi Isurugi and Nariaki Utsumi's Hazard Level, as evidenced by their usage of the Transteam Gun.
4 The minimum Hazard Level required to use the Sclash Driver. Ryuga's latest known Hazard Level as measured by Blood Stalk The Forbidden Item
4.2 Kazumi Sawatari's current 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
4+ Gentoku Himuro’s Hazard Level, as evidenced by his usage of the Sclash Driver.


  • 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.