how does flash point relate to the out of service fuel concentration

[hollerg]

Our plant handles methanol and xylene and I would like your thoughts on the practices used when cleaning the tanks. They fill and drain out the water and then run a flashpoint on the residual water (~ 100 F) judging the tank is clean and air can be admitted into the tank when the flashpoint is above 200 F, rather than sampling the vapor space and determining that the concentration is below the Out of Service Fuel Concentration (OSFC) as determined from the fire triangle.

How does the flashpoint relate to the OSFC, for the methanol/water case and for the xylene/water case?

Any hidden pitfalls to using the flashpoint in place of the OSFC? What restriction to adopting that approach should be applied?

 

[georgeverghese]

Methanol vapor would be very soluble in water, so given sufficient contact time and adequate turbulence in the water, a sample withdrawn from the liquid phase would enable a true picture of the flash point wrt to methanol.

Xylene vapor however, is only very slightly soluble in water, so a water sample would give a very poor indication of how much xylene there is in the vapor space. This is because the error in concentration readout in the liquid phase would normally be such that you would get a false picture of the xylene concentration in the vapor space....unless you have a device or procedure that gives you a high resolution concentration estimate.