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The Probable Maximum Loss (PML) report is a tool used to evaluate a building’s likely damage during a significant seismic event.

This site is published by Partner Engineering and Science, a major nationwide provider of PML Reports . The purpose of this site is to promote use of the best engineering practices in completing PML Reports.

ASTM Standards: In 2007, the American Society for Testing Materials (ASTM) updated its Standard for PMLs and published a new standard on PMLs. ASTM E 2026-2007 This standard serves as the great tool box for PMLs. It allows for many different types of PMLs and permits the engineer to report the PML in various ways. The PML is a tool used by many industries, which all have separate and distinct ways of evaluating risk.

This standard focuses on reporting seismic risk to the financial industry. The ASTM E 2557 Standard requires engineers to report the Scenario Expected Limit (SEL), Design Building Earthquake as the PML.

 Beyond ASTM The ASTM sets only the minimum standards to be met for PMLs. These base standards are not stringent enough to provide lenders with the consistency, transparency, and sound engineering judgment necessary for a cogent PML. To achieve these goals, lenders need to ask for more than ASTM compliant PMLs . Here are some guidelines:

  1. While ASTM does not specify a mathematical method for calculating the PML, the best choice is the Thiel Zsutty Method. To ensure transparency and reviewability, engineers should show their mathematics.
  2. Engineers should explain how they arrived at values for each of the input values into the Thiel Zsutty equation. Again, the more these values are discussed the more peer reviewable and transparent the reports will become.
  3. Engineers should provide a thorough discussion of building systems and their ability to bear load. If the PML is high, the engineer should provide a clear description of the building’s defects.
  4. New ASTM Standards do not specify that PMLs be performed by registered civil or structural engineers. However, because a high level of engineering judgment is essential to carrying out PMLs, hiring a registered engineer is crucial. Their certifications ensure that they are professionals possessing the requisite knowledge and skill to produce a reliable PML.