SRE Best Practices Practical By Samson Tanimawo, PhD Published Jun 19, 2026 4 min read

The Blast Radius Classifier for Every Change

Every change should be classified by blast radius before it ships. The five-tier classifier and the gates each tier triggers.

The five tiers

T0: dev-only. No customer impact. No gates.

T1: internal users. Light gates: PR review.

T2: opt-in customers. Full gates: PR review, eval, canary.

T3: all customers, single region. Heavy gates: above + on-call awareness, deploy window.

T4: all customers, all regions. Critical gates: above + leadership awareness, two-person approval.

The author classifies the change; reviewer verifies. Disagreements escalate.

Misclassification is a postmortem. Severe misclassification (T4 shipped as T1) is a major incident.

Calibration: monthly review of last month's changes. Were classifications accurate?

Tier inflation: marking everything T2 to avoid scrutiny. Defeats the system.

Tier deflation: marking T4 as T2 because the author 'knows' it is safe. The classifier is for the team, not the individual.

Skipping the classifier on 'urgent' changes. Urgent changes are exactly when the classifier is most useful.