How to Evaluate Boiler Explosions

Explosions in boilers are not uncommon. Irrespective of the type of fuel being fired, boilers have experienced explosions. Remember that an explosion analysis is not a fault finding mission, but a fact finding one for prevention of the cause in future. Never officially put on record any of your findings before the chief of the plant at the highest level agrees with you. There are many areas to be taken care by the plant owner and you as a fact finding man have to be helping him in all. However it is very important to record all the facts for your analysis and corrective / preventive action.

• Reach the site as early as possible (before any evidence is destroyed).
• Take all printouts of all recorded parameters from at least 24 hrs before the explosion.
• Take the first-up details; take the event recorder data if available.
• Take photos of the entire area while inspecting the boiler.
• Look at all the areas, starting from FD fan to ID fan make a full survey.
• Immediately pick up any evidence samples then and there and tag them as to where you got them and how they were positioned; take photos before disturbing the position.
• Take the copy of the shift and boiler operator log book.
• Discuss with all starting from the chief of boiler and plant to the local floor operator. Note all points verbatim.
• It will be good to talk to the maintenance group, both regarding the maintenance carried out and their impression about operation.
• Look at the available after-combustion products before they are cleaned; take samples for analysis.
• Look at the start-up and shut down procedures as explosions happen mainly during this period.
• Mark all deviations from
  • Safe practices
  • Good operating practices
  • Large load swings
  • Any fuel interruption
  • Action by operator to save unit from tripping like introducing high reactive fuel
  • Action by local operator without instruction from main control room like introducing igniter
  • Contradictions in statement of persons
  • Observation that can be a possible source of evidence
  • Any other points for your analysis
  • Make up your own hypothesis for the explosion with the evidence collected; build up a model
  • Validate this with the owner and the designers
  • Check with the codes like NFPA whether your hypothesis for explosion of boiler fall in line with these codes and make the final report

NFPA (National Fire Protection Association) and others have analysed the causes of explosion and find that operator error (can be more clearly put as operator anxiety to save unit from trip) has contributed to about 47%, insufficient purge about 39%, control failure 11%, and equipment failure 3%. The only way to avoid an explosion is to avoid the accumulation of fuel in the boiler.