Sudden Release of Chlorine Gas ("Puff)

 

Chlorine Toxic Gas Properties and Standards

 

Chlorine  Cl2  Molecular Weight = 70.91              1 ppm = 2,900 microgram/m3  

 

Chlorine Permissible Exposure Limit = PEL = 0.5 ppm or 1,450 microgram/m3 for 8 hr average conc.

 

Washington State Acceptable Source Impact Level (ASIL) = 10 microgram/m3 for 24 hr average conc

 

Short Term Exposure Level = STEL = 1 ppm = 2,900 microgram/m3 = 0.0029 gm/m3 for 15 minutes

 

ERPG-2 = Emergency Response Planning Guideline from Am Industrial Hygiene Association    

ERPG-2 = maximum airborne concentration below which it is believed nearly all people could be

                 exposed for up to 1 hour without experiencing serious health effects or symptoms

 

Chlorine ERPG-2 = 3 ppm for 10 minute average     http://www.epa.gov/ttn/atw/hlthef/chlorine.html

 

Fatal Exposures:   430 ppm Cl2  for 30 minutes       1,000 ppm Cl2  for 2 minutes

 

Example Problem

Given:

Instantaneous gaseous emission (puff) of 100 lbs (45,360 grams) chlorine   sigma

Emission height of 5 meters

Initial horizontal dispersion coefficient = sigma y = 1 meters

Initial vertical dispersion coefficient = sigma z = 1 meters

 

Find:

a.  Maximum 15 minute average chlorine concentration

b.  Downwind distance to maximum ground level 15 minute chlorine concentration

c.  Atmospheric stability class for the maximum ground level concentration

d.  In order to protect the public, what distance from the chlorine emission point should

       the fence be located for public safety?

 

TSCREEN Inputs

  Gaseous Release Type

  Discharge from Equipment Openings

  Release Height Above Ground = 5 meters

  Initial Lateral Dispersion Coefficient = 1 meter

  Initial Vertical Dispersion Coefficient = 1 meter

  Fenceline distance = 10 meters (note TSCREEN will not allow fenceline distance less than 10m)

  Conc Averaging Time for Graph = 15 min

 

TSCREEN Printout is shown below:

 

 100 lb Gaseous Chlorine Leaked                                                 April 18, 2004

 

    TOTAL AMOUNT OF MATERIAL RELEASED (G):   .4536E+05

          RELEASE HEIGHT ABOVE GROUND (M):      5.000   

 INITIAL LATERAL DISPERSION SIGMA (Y) (M):   1.000   

INITIAL VERTICAL DISPERSION SIGMA (Z) (M):   1.000   

 

 ******************************************************

 ***         SUMMARY OF PUFF MODEL RESULTS          ***

 ******************************************************

 

THE MAXIMUM CONCENTRATION AND THE DISTANCE TO MAXIMUM

CONCENTRATION FOR DISTANCES BEYOND FENCELINE    .010 (KM).

FOR NEAR SURFACE RELEASE MAXIMUM CONCENTRATION WILL OCCUR AT

THE FENCELINE.

 

    AVERAGING           MAXIMUM                     DISTANCE TO          STABILITY

    TIME (MIN)     CONCENTRATION (G/M**3)   MAX. CONC. (KM)     CLASS

 

 INSTANTANEOUS        2.017E+02                        .010                             U

       1                              1.421E+01                         .013                             U

       5                              2.842E+00                         .013                             U

*      15                           9.473E-01                          .013                             U

       60                            2.368E-01                          .013                             U

 

 ******************************************************

 **   REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS  **

 ******************************************************

 

 *********************************

 ***      PUFF DISTANCES       ***

 *********************************

 

 THE MAXIMUM CONCENTRATION AS A FUNCTION OF DOWNWIND DISTANCE

 AND THE CONDITIONS THAT PRODUCED THE MAXIMUM AT THAT DISTANCE.

 

 MIXING HEIGHT (M)   320.

 WIND SPEED (M/SEC)    1.0

 

 AVERAGING                         DOWNWIND DISTANCE (KM)

 TIME (MIN)   MAXIMUM CONCENTRATION (G/M**3) AT VARIOUS DOWNWIND DISTANCES.

                  STABILITY CLASS THAT PRODUCED THE MAX. LISTED BELOW

             0.01                0.03              0.05             0.07             0.1               0.5

 ==========================================================================

 INST.   2.017E+02   5.872E+01   5.490E+01   5.073E+01   3.552E+01   1.076E+01

                   U                 U                 N               N                N                   S

 

 1          1.316E+01    8.254E+00   5.570E+00   6.709E+00   6.351E+00   2.317E+00

                   U                 U                 N               N                N                  S

 

 5          2.632E+00   1.651E+00   1.114E+00   1.342E+00   1.270E+00   4.635E-01

                   U                 U                 N               N                N                  S

 

*15       8.773E-01   5.503E-01   3.713E-01   4.473E-01   4.234E-01   1.545E-01

                   U                 U                 N               N                N                  S

 

 60        2.193E-01   1.376E-01   9.283E-02   1.118E-01   1.059E-01   3.862E-02

                   U                 U                 N               N                N                  S

 

 AVERAGING                         DOWNWIND DISTANCE (KM)

 TIME (MIN)   MAXIMUM CONCENTRATION (G/M**3) AT VARIOUS DOWNWIND DISTANCES.

                  STABILITY CLASS THAT PRODUCED THE MAX. LISTED BELOW

                    1.0               3.0              5.0              7.0            10.0           30.0

 ==========================================================================

 INST.   6.748E+00   1.052E+00   3.548E-01   1.674E-01   7.407E-02   5.638E-03

                     S                 S                 S                 S                S                S

 

 1          2.650E+00   8.442E-01   3.231E-01   1.589E-01    7.203E-02    5.618E-03

                     S                 S                 S                 S                S                  S

 

 5          5.307E-01   2.187E-01   1.162E-01    7.363E-02     4.320E-02    5.121E-03

                     S                 S                 S                 S                S                  S

 

*15       1.769E-01   7.291E-02   3.874E-02   2.466E-02     1.498E-02    2.973E-03

                     S                 S                 S                 S                S                   S

 

 60      4.423E-02     1.823E-02    9.685E-03    6.164E-03   3.746E-03     7.581E-04

                     S                 S                 S                 S                S                    S

 

 STABILITY CLASSES   U = UNSTABLE     N = NEUTRAL     S = STABLE

 

 * INDICATES AVERAGING TIME THAT WAS SELECTED FOR PLOTTING

 

 

********************************

*** END OF PUFF MODEL OUTPUT ***

********************************

\

Answers:

a.  Maximum 15 minute average chlorine conc   9.473E-01 = 0.9473 gm/m3 = 947,300 microgram/m3 = 326.66 ppm

b.  Downwind distance to maximum ground level 15 minute chlorine concentration  = 0.013 km = 13 meters 

c.  Atmospheric stability class for the maximum ground level concentration    Unstable

d.  In order to protect the public, what distance from the chlorine emission point should

       the fence be located for public safety?       Fence needs to be downwind of STEL: Conc = STEL

       = 1 ppm  = 0.0029 gm/m3 for 15 minutes which is roughly at a distance of 6 km = 6,000 meters.

 

EPA has “Risk Management Plan” Software which can be used to estimate the distance from a potential hazardous and toxic gas release into the atmosphere to a safe location.  The website is at http://yosemite.epa.gov/oswer/ceppoweb.nsf/content/rmp-comp.htm

 

RMP*Comp is a free program you can use to complete the offsite consequence analyses (both worst case scenarios and alternative scenarios) required under the Risk Management Planning Rule, which implements Section 112(r) of the 1990 Clean Air Act.

RMP*Comp helps you complete offsite consequence analysis that is required under the Risk Management Program. When you use RMP*Comp, (a) you don't need to make any calculations by hand (you just enter necessary information, such as the amount of a chemical stored in a vessel), and (b) the program guides you through the process of making an analysis.