3 replies to this topic

[process85]

Hi everybody

I am currently preparing Safety process data for Hazardous Area classification.

While peparing that I am not able to judge whether a particular equipment is flammable or not.
Because as per NFPA ,flammability limits given are concentration in air .And i have stream summary which gives me concentration in the mixture of process streams.
As i m working on a Sulfur Recovery unit,i have many flammable components such as H2S,Sulfur,
H2,COS .But all of them are present in different concentrations in different equipments(sometimes even ppm concentration).

And in some cases H2S is even present in dissolved in H2O.

Does that mean i have to classify each equipment as flammable for hazardous area classification?

This might be a very elementary question for some of you ,but please guide me with whatever knowledge u can share on this topic.

[ankur2061]

process85,

Hazardous area classification is based on dispersion of flammable chemicals in air. It also includes the partial pressure of flammable chemicals if dissolved in a liquid.

Flammability limits in chemical process industry parlance is expressed in terms of LEL or LFL (Lower Explosive or Flammability Limit) and UEL or UFL (Upper Explosive or Upper Flammability Limit). The LEL and UEL is defined in terms of the volume percentage of the gaseous chemical in air. Below the LEL concentration or above the UEL a fire cannot be sustained.

For H2S, following are the flammability limits:

LFL: 4.3% by vapor in air

UFL: 46% by vapor in air

Data is from Appendix A of 'API RP 49, 3rd edition, May 2001.

Hope this helps.

Regards,
Ankur.

[process85]

Thanks ankur

Sorry for my delayed reply. But i m still not clear regarding the subject.

What your reply states, is already given in NFPA 325 & OISD 113 and all LFL & UFL values are also given.

But my concern is having known concentration of a flammable material in process mixture,can we predict whether this much amount of flammable substance is capable of making a mixture with air between limits LFL & UFL.

[Qalander (Chem)]

Thanks ankur

Sorry for my delayed reply. But i m still not clear regarding the subject.

What your reply states, is already given in NFPA 325 & OISD 113 and all LFL & UFL values are also given.

But my concern is having known concentration of a flammable material in process mixture,can we predict whether this much amount of flammable substance is capable of making a mixture with air between limits LFL & UFL.

Dear process85 Hello/Good Afternoon,
Visit www.csb.gov or www.chemsafety.gov you may find some useful info
Regards
Qalander