There'll be some specific rules regarding how the powers work. Unless there's an exceptional case then here is the general rules of thumb:

1. Greater powers mean you were more severely exposed to the chemicals (ie closer to the explosion).
2. Usually, those closer to the epicenter of the incident are more likely to suffer mutations or other side effects to their powers. A power like having Herculean strength might come at the cost of being mutated into a beast-person, for example.