Hot Work Permit Calculator

Example Data Table

These examples are illustrative; always apply your site rules and approvals.

Formula Used

This tool calculates a Hot Work Risk Score on a 0–100 scale using a weighted model:

• Risk Score = Base(work type) + Duration + Area + Proximity + Fuel load + Readings + System status − Control credits
• Proximity adds more risk when combustibles are closer.
• Readings add points for higher LEL and abnormal oxygen.
• Controls subtract points (fire watch, extinguisher, ventilation, isolation, containment, PPE, approvals).

Decision thresholds: Low (<40) approved, Medium (40–69.99) approved with extra controls, High (≥70) denied until mitigations.

How to Use This Calculator

1. Enter job details, work type, area, and expected duration.
2. Record distances to combustibles and note any flammable liquids.
3. Provide gas test method and readings (LEL and oxygen).
4. Select site protection status and controls (fire watch, extinguishers, isolation).
5. Click Calculate Permit to view decision and guidance.
6. Download CSV or PDF for documentation, briefings, and audits.

Safer permits reduce fires, downtime, and costly injuries everywhere.

1) Why permits matter on construction sites

Hot work—welding, cutting, grinding, and torch tasks—creates ignition sources that can start fires in minutes. A permit process turns routine jobs into controlled operations by documenting hazards, assigning responsibilities, and confirming that protective systems are working before sparks fly.

2) Setting a practical hazard baseline

Begin with the work type, duration, and location. Enclosed rooms and process areas often carry higher ignition and smoke-travel risk than open spaces. Longer work increases exposure time, so even “normal” tasks can become higher risk when the job extends across shifts or multiple trades.

3) Managing combustibles and separation distance

Distance to combustibles is one of the strongest predictors of incident potential. Many sites use a 10 m rule of thumb where feasible, with additional shielding when removal is not possible. Include dust, packaging, insulation, wooden formwork, and hidden voids in the fuel assessment.

4) Gas testing and atmosphere readings

Atmospheric testing should match the environment. “Before work only” may be insufficient where vapors can migrate. This calculator highlights elevated LEL values and abnormal oxygen outside roughly 19.5%–23.5%. If readings trend upward, stop work, ventilate, and retest until stable and acceptable.

5) Fire protection system readiness

A permit should explicitly state whether sprinklers, detection, or alarms are impaired or isolated. When protection is reduced, compensating measures become mandatory—extra extinguishers, tighter watch, shorter validity, and escalation approvals. Document who authorized the impairment and when normal service will be restored.

6) Controls that reduce risk the most

Consistent controls prevent repeat incidents: a trained fire watch, verified extinguisher availability, spark containment, hot work screens, ventilation, and complete isolation/LOTO of nearby energy sources. Securing gas cylinders and confirming PPE prevent secondary injuries and reduce chaos if the job environment changes unexpectedly.

7) Permit validity and post-work monitoring

Shorter permits force re-checks when conditions shift. This tool recommends a validity window between 1 and 8 hours based on the risk score and controls. Post-work monitoring is critical—many programs require a fire watch for at least 30 minutes after completion, longer where hidden spaces exist.

8) Using the risk score for consistent decisions

A transparent scoring model improves consistency across supervisors and shifts. Scores below 40 generally indicate routine control readiness, 40–69.99 signal extra measures and tighter oversight, and 70+ indicates mitigation is required before authorization. Export the record to support audits, handovers, and toolbox talks.

1) Does this calculator replace my company permit form?
No. It helps standardize hazard review and documentation. Always follow your site’s approved permit template, approvals, and legal requirements, then attach exported results as supporting evidence.

2) What should I enter for fuel load?
Rate how easily materials can ignite nearby. Low means mostly noncombustible surroundings. High includes dust, packaging, timber formwork, insulation, solvents, or clutter that could catch sparks.

3) When should gas testing be continuous?
Use repeated or continuous testing where vapors can migrate, ventilation is uncertain, or the job is in a confined or process area. If readings change, pause work and correct conditions before restarting.

4) Why is oxygen outside 19.5%–23.5% flagged?
Low oxygen can indicate displacement hazards, while high oxygen can accelerate combustion. Both conditions can change how quickly a small ignition turns into a major fire event.

5) What if combustibles cannot be moved beyond 10 meters?
Apply compensating controls: fire-resistant covers, spark mats, screens, wetting where appropriate, and an upgraded fire watch. Tighten permit validity and add management approval when exposure remains high.

6) What makes a fire watch “effective”?
A trained person with no other duties, clear stop-work authority, and direct access to extinguishers and communications. They should monitor during work and for the required after-work period.

7) Can I download CSV/PDF without recalculating?
Downloads use your most recent submitted calculation stored in the session. Recalculate whenever conditions change—location, duration, readings, impaired systems, or control selections—to keep the record accurate.