Fire/Explosion Protection

CSB Issues Safety Alert

By Chemical Processing Staff

Aug 17, 2016

The U.S. Chemical Safety Board, Washington, D.C., has just released “CSB Safety Alert: Preventing High Temperature Hydrogen Attack (HTHA)” in an effort to prevent accidents like the 2010 fatal explosion and fire at the Tessoro refinery in Anacortes, Wash., that injured 7 workers.

The CSB’s 2014 report placed the blame for the accident on the failure of a 40-year-old carbon-steel heat exchanger that was caused by HTHA. The CSB recommended that the American Petroleum Institute (API) better address the threat of HTHA. The API recently issued updated guidance.

However, the CSB found this inadequate.

“Updated guidance covering this issue — recently published by API — provides incremental improvements, but it fails to address important elements of the CSB’s recommendations. The standard uses what are referred to as ‘Nelson Curves’ to predict the operating conditions where HTHA can occur in different types of steels. The curves are based on process data voluntarily reported to API, and are drawn beneath reported occurrences of HTHA to indicate the ‘safe’ and‘unsafe’ operating regions.

“API’s updated carbon steel Nelson Curves do not take into account all of the estimated process conditions where the catastrophic failure occurred due to HTHA at the Tesoro Anacortes Refinery. As a result, the new curves allow refinery equipment to operate at conditions where HTHA severely damaged the Tesoro heat exchanger. The use of a curve not incorporating significant failure data could result in future catastrophic equipment ruptures.”

The CSB’s chair, Vanessa Allen Sutherland, noted:

“In the absence of industry guidance that incorporates findings from the Tesoro Anacortes failure, the CSB is issuing a safety alert to provide additional direction for industry.”

The safety alert advises companies to:
1. Identify all carbon steel equipment in hydrogen service that has the potential to harm workers or communities due to catastrophic failure;
2. Verify actual operating conditions (hydrogen partial pressure and temperature) for the identified carbon steel equipment;
3. Replace carbon steel process equipment that operates above 400 °F and greater than 50 psia hydrogen partial pressure; and
4. Use inherently safer materials, such as steels with higher chromium and molybdenum content.

For more details on this alert, go to:

For information on Sutherland’s plans and goals for the CSB, see “Chemical Safety Board Opens Up.”