Corporations spend enormous amounts of money on explosion investigations. Yet experienced investigators know there are only 9 ignition sources. For an actual asphalt tank fire, the analysis is shown below and whether or not this ignition source was ruled out.
Column 1 is labeled: What facts do we know about the incident
Column 2 is labeled: What facts don’t know about the incident
Column 3 is labeled: The ignition sources which you can see below
List of Ignition Sources
|Ignition Source||Analysis||Ruled Out?|
|Autoxidation||No fibrous material that could wick hydrocarbons was present. Autoxidation is the ‘rag in the garage’ ignition where there is a high hydrocarbon surface area to oxygen ratio. Typically occurs in storage tanks when hydrocarbons spill onto fiberglass insulation.||Ruled out|
|Autoignition||Occurs when hydrocarbon/air mixture derive enough energy from surroundings to ignite.
· Air entered the day tank during a pump down and fill cycle of the day tank
· Temperature in tank was well above autoignition temperature for several hydrocarbon components typically in vapor space
|Most likely ignition source|
|Catalytic Material||Typical catalytic material to cause combustion is pyrophoric iron sulfide.
· Tank was cleaned in December
· Tank lid was confirmed clean by the writer after removal other than post explosion splash of asphalt when foam was added
· Therefore, no pyrophoric iron sulfide was present
|Electrical Arcing||No arcing electrical equipment exists near or in the tank.||Ruled out|
|Static Charge||Incoming flux from flux tank drops from the end of the dip tube to the bottom of the tank 23 feet. Free falling liquids are considered to be a possible cause of static charge buildup in a tank but this dip leg has functioned without an ignition for many years and asphalt does not represent a static charge hazard.||Ruled out|
|Friction||No mechanical equipment present in the vapor space that could cause high heat from parts rubbing.||Ruled out|
|Compression||Atmospheric tank compression of gases for heat up not likely since there is nothing in tank to cause compression.||Ruled out|
|Coke/ Carbon||· Tank was cleaned in December 2003
· Tank lid was confirmed clean after removal other than post explosion splash of asphalt when foam was added
· Therefore, no coke/carbon was present
|External Flame Source||No flame source present at the top of the day tank.||Ruled out|
With the three column method of investigation, the ignition source can be quickly found which leads to the rapid determination of the root cause of the explosion.
Usually in chemical plants and refineries which are group D class 1 Division 2, open flames are not present nor is cigarette smoking allowed so an external flame source is quickly ruled out.
Asphalt in this case does not hold a static charge. This was quickly ruled out.
Using the MindManager software, the three columns are clearly shown and how one or more items in column 1 rule out an ignition source in column 3. Connections in column 1 and column 3 are made with the software for easy understanding. These connections can be challenged by the leader working on the explosion investigation or by the people working on the explosion investigations team. Complete analysis is beyond the scope of this blog.