Adding Representative Fluids

This article provides guidance for adding new Representative Fluids to Newton RDMS.

Determine Fluid Type

There are four types of fluids used by RBI models:

  • Flammable - In literature, a distinction is made between flammable and combustible fluids. Both indications are considered ‘flammable’.
  • Toxic - A fluid is considered toxic when exposure to an airborne concentration causes irreversible or other serious health effects, or symptoms that could impair an individual’s ability to take protective action. A fluid is not considered toxic for the RBI models when the negative health effect results from ingestion or when the fluid is considered to be carcinogenic to humans.
  • Reactive - A fluid that is neither flammable nor toxic but can cause injury to humans by chemical or thermal burn.
  • Inert - A fluid that does not meet the definition of flammable, toxic, or reactive fluid. This type of fluid is not known to cause serious health effects in humans or harm to the environment.

If a fluid is equally flammable and toxic, then create two Representative Fluids: one with flammable parameters and the other with toxic parameters. The fluid names should distinguish between fluid types. An EXCEL file 'Representative Fluid Data' is attached (see bottom of page) for documenting fluid parameters for each new Representative Fluid. 

If the process stream includes a mixture of flammable and inert materials or multiple flammable materials, then a single flammable fluid can be created that represents the mixture. The EXCEL file provides a way to combine a flammable and inert or two flammable components based on weight percentage. 

Gather Fluid Parameters

The fluid parameters required for the RBI models are listed in the table below. The EXCEL file includes formulas to calculate some of the parameters. When gathering fluid parameters, take special note of the required unit of measure. When using the EXCEL file, save a copy for each Representative Fluid and use it to document the source for each parameter. 

Parameter Description SAE UOM Metric UOM F T R Notes
Molecular Weight Molecular Mass g/mol g/mol X X X  
Liquid Density Density of Liquid Phase lb/cu. ft. g/cm3 X X X 1,2
CP/CV Ratio of Specific Heats - - X X   3
Boiling Point Boiling Temperature F C X X    
Buoyancy Density of Vapor Compared to Air (Buoyant or Dense) - - X X    
PFF Pool Fire Factor for Flammable Liquids - - X     4,5
HCF Heat of Combustion kJ/kg kJ/kg X      
LFA Liquid Factor Ambient - -   X   6
LFB Liquid Factor Boiling - -   X   7,8
Endpoint Toxic End Point mg/l mg/l   X   9
Flash Point Flash Point Temperature (Closed Cup) F C X      
AIT Auto Ignition Temperature F C X      
PigF Probability of Ignition at the Flash Point Temperature - - X     10

The 'X' in columns F, T, and R indicates the parameter is required for Flammable, Toxic or Reactive fluids.


  1. In some documents, the metric unit for liquid density is listed as mg/l (milligrams per liter). This unit is incorrect for the RBI models; the correct metric unit for liquid density is g/ml (gram per milliliter) which is equal to g/cm3 (gram per cubic centimeter). For reference, water has a density of about 1.0 g/ml and 1,000,000 mg/l.
  2. The liquid density should be given at 77 ºF / 25 ºC. Even when at that temperature the fluid is a gas at atmospheric pressure, the liquid density should be entered, not the gas density.
  3. A reliable source for the ‘Ratio of Specific Heats’ is NOAA
  4. If the PFF is not available in the published literature it can be calculated using the Heat of Vaporization, Heat of Combustion and the Liquid Heat Capacity. The equation is given in the Representative Fluid spreadsheet. Please note that the Heat of Combustion has the unit kJ/kg and the Heat of Vaporization and Liquid Heat Capacity have respectively the units of measure J/kg and J/kg-K. The equation to calculate the PFF converts the Heat of Combustion from kJ/kg to J/kg.
  5. The PFF for all Reactive fluids is 0.564.
  6. If the LFA is not available in the published literature (EPA RMP) it can be calculated using the Vapor Pressure and the Molecular Weight. An equation is given in the EXCEL 'Representative Fluid Data'.
  7. If the LFB is not available in the published literature (EPA RMP) it can be calculated using the Boiling Point and the Molecular Weight.
  8. The Liquid Factor Boiling is shown as LBF in the lookup table RBI_FLUID_DATA. The correct abbreviation is LFB.
  9. The preferred sources for toxic endpoint data are the EPA-RMP data and ERPG-2 values from AIHA. It can also be estimated from IDLH and LC-50 toxicity data. When the EPA or ERPG-2 data is available, this toxic endpoint data shall be used. Second in preference is the IDLH data. The endpoint equals to 0.1 * IDLH. Third in preference is the LC50 data. The endpoint equals to 0.01 * LC50. When multiple LC50 values are reported, the lowest LC50 value shall be used. Don’t confuse the LC50 value with LD50. Equations are suggested to convert LD50 values to an endpoint, however the units don’t match in this conversion and LD50 is reported with many different units. It is suggested not to determine an endpoint value from LD50 values. Two reliable sources for toxic endpoint are:
    U.S. Department of Energy:  
  10. The PigF is an estimated value based on experience and judgment. Examples of PigF values are: H2 = 1, C1-C4 = 0.5, C5-C8 = 0.25, C9-C25 = 0.10 and Glycol = 0.01.

Add Fluid to RDMS

In Newton RDMS, go to Admin Lookups and search for 'RBI_FLUID_DATA'. Add a new row to the lookup table and enter a value in every cell. If a parameter does not apply because of the fluid type, then re-enter a zero in that cell. When finished, press save.