Inherent Safety & Security Index for Toxic Inhalant Hazardous Chemicals

Transcription

1 Inherent Safety & Security Index for Toxic Inhalant Hazardous Chemicals Dr. Ray Mentzer Mary Kay O Connor Process Safety Center 2010 International Symposium Artie McFerrin Department of Chemical Engineering Texas A&M University October 26, 2010 The Mary Kay O'Connor Process Safety Center gratefully acknowledges the support for this work by the Department of Homeland Security, Chemical Security Analysis Center through contract TCN W911NI-07-D-0001, DO#

2 Education - MKOPSC Process Safety is part of the Chemical Engineering core curriculum at Texas A&M +1,100 students have taken course Safety Engineering Certificate, requires five courses 106 undergraduates have completed 48 students have received advanced degrees through MKOPSC Numerous continuing education courses +2,675 trained domestically & internationally 2

3 Active Research Areas Reactive Chemicals Flammability of Aerosols and Liquid Mixtures LNG Safety Research Micro-Calorimetry System for Explosives Detection Dust Explosions Facility Siting and Layout Integration of Safety Issues in Solvent Optimization Incident Risks in Chemical Process Industry Quantitative Risk Assessment Resilience Engineered Systems Security Related Studies 3

4 Measurement of Inherent Safety & Security Several methods have been proposed in the literature for measuring the degree of inherent safety of a chemical or process Dow Fire & Explosion Index (1,2); Chemical Exposure Index (3) Mond Fire, Explosion & Toxicity Index (4) Edwards & Lawrence (5) Others Heikkila (6), Shariff (7), Mannan & Bily (8), etc Unfortunately none have been widely accepted by industry, perhaps due to complexity and difficulty of use + Nor do they address security related implications A simple quantitative metric is needed to assess change in safety & security related risks with process alternatives, changes in operating conditions, etc. + Specific focus on toxic inhalant hazardous chemicals in Appendix A of the Chemical Facility Antiterrorism Standards Regulations (9) 4 4

5 Development of ISSI Proposed semi-quantitative inherent safety & security index (ISSI) Based on chemical properties, operating conditions & number of potentially impacted people Numerous properties were examined, resulting in: o Chemical properties: LC50 toxicity available for 49 chemicals of interest for a specific exposure time and chosen over IDLH, AEGL, ERPG, etc Vapor density relative to air is useful indicator of tendency to rise / dissipate; chosen over vapor pressure & boiling point 5 5

6 Development of ISSI cont d Properties cont d: o Operating conditions: Temperature scaled as a function of maximum operating temperature and normal boiling point T f = (MOT-BP)/BP Pressure scaled as function of maximum operating pressure and vapor pressure at standard conditions P f = ln [(MOP VP)/VP] Stored volume hazard increases with mass stored o Distance to toxic endpoint: Key measure of the impact of a release Determined from RMP Comp software (10) based on threshold quantity, concentration, release temperature, assumed meteorological conditions, setting & fluid state 6 6

7 Development of ISSI cont d Properties cont d: o Number of affected persons Key measure of off-site impacts Determined from Landview (11) software with geospatial population data once DTE has been calculated Each of the seven variables is assigned a value of 1 to 5, based on range of values per table on following page (e.g., LC50 <30, assigned 5; No. of Affected People<100, assigned 1) Thus, the higher the assigned value the higher the safety or security hazard Recognizing this is the hazard inherent to the process and does not reflect the likelihood or frequency of an event (needed to determine true risk ) 7 7

8 Index Values For Property Ranges EXTENT OF CHEMICAL AND PROCESS HAZARDS Number of Affected Persons Chemical specific Operations specific Priority Index LC50, 4 hr rat (ppm ) VD Relative to air (1) Quantity (Lbs) Tf (unitless) Pf (unitless) DTE (miles) NAP 1 >701 <1.0 <1,500 <0.2 <1 < ,500-2, ,000-4, ,000-9, ,000 9, ,000-99,999 5 <30 >=4.0 >10,000 >5.0 >2.5 >25 >100,

9 Steps In Implementing the Index 1 The chemicals or process steps to be compared are identified, with emphasis on consistent process boundaries among the process alternatives 2 Compile physical and toxicological properties of TIH chemical(s) involved in the process (e.g., LC50, vapor density, boiling point, vapor pressure) 3 - Identify process & storage vessels with large volumes of chemical(s) of interest + calculate DTE for largest volume, including alternatives being compared 4 Determine number of potentially affected people using LandView 9

10 Determining The ISSI Once seven terms / parameters are identified multiply each by weighting factor and sum, yielding the ISSI index o weighting factors are assigned to each parameter based on difference in a given parameter value between process alternatives (e.g., LC50) o weighting factor is 1.0 if index parameters are the same, 2.0 if the index parameters differ by one, etc. Overall ISSI is determined by summing ISSI values determined for each TIH present in process o Could extend to mixtures in this manner, but data not available for validation 10

11 Ammonia Supply Case Study Comparison of anhydrous liquid, aqueous and vapor ammonia for transport via a piping system to a catalytic reactor. (12) Chemical Anhydrous Liquid NH 3 Aqueous NH 3 23% Anhydrous Vapor NH 3 Parameter Anhydrous Liquid NH 3 Aqueous NH 3 23% Anhydrous Vapor NH 3 LC50 [ppm 4 hr-rat] Vapor density [Air=1] Vapor pressure [atm] Boiling Point [K] LC50 Vapor density Quantity stored Max. Op. T [K] Max. Op. P [atm] Tf Pf= Ln(MOP-VP/VP) Quantity stored [lb] DTE [miles] NAP Tf DTE NAP Pf ISSI ISSI with weighting factors

12 Methyl Isocyanate (MIC) Case Study Comparison of MIC at original Bhopal facility conditions, incident conditions & DuPont alternative process (2, 13-17) MIC (Bhopal) MIC (Bhopal) Chemical, Normal Op.) incident) LC50 [ppm 4 hr-rat] MIC (DuPont, 1994) Vapor density [Air=1] Vapor pressure [atm] Boiling Point [C] Max. Op. T [C] Max. Op. P [atm] Tf Pf= Ln(MOP-VP/VP) Quantity stored [lbs] DTE [miles] >25 > NAP >100,000 >100,000 >10,000 Main driver for DuPont process index is reduction in quantity stored Chemical MIC (Normal Op.) MIC (incident) MIC (Dupont tech.) LC Vapor density Quantity stored Tf Pf DTE NAP ISSI ISSI with weighting factors

13 Wrapup Conclusions Concept of an inherent safety index has been extended to include security, and potential impacts beyond plant fence Semi-quantitative methodology has been demonstrated with case studies Recommendations Further study of methodology using additional case studies Apply to chemicals beyond 49 TIH CFATS App A chemicals Apply to mixtures Examine ISSI functionality: Explore limitations of pressure scaling factor Examine benefits of weighting factors Consider heat of reaction as an additional parameter, with potential common contaminants such as water, moisture, air, etc 13 13

14 References 1. Khan, F. l.; Sadiq, R.; Amyotte, P. R., Evaluation of Available Indices for Inherently Safer Design Options. Process Safety Progress 2003, 22, (2), Mannan, S., Lees' Loss Prevention in the Process Industries. 3 ed.; Elsevier: 2005; Vol AIChE, Dow's Chemical Exposure Index Guide. First ed.; American Institute of Chemical Engineers: New York, NY, USA, ICI, The Mond Index. How to identify, assess and minimise potential hazards on chemical plant units for new and exisiting processes. 2 ed.; United Kingdom, Edwards, D. W.; Lawrence, D., Assessing the Inherent Safety of Chemical Process Routes: Is There a Relation Between Plant Costs and Inherent Safety? Trans IChemE 1993, 71, (Part B), Heikkilä, A.-M. Inherent safety in Process Plant Design. An index-based approach. Technical Research Centre of Finland, Espoo, Finland, Shariff, A. M.; Rusli, R.; Leong, C. T.; Radhakrishnan, V. R.; Buang, A., Inherent safety tool for explosion consequences study. Journal of Loss Prevention in the Process Industries 2006, 19, Mannan, M. S.; Bily, V. J., Risk ranking methodology for development of prioritization rationale and determination of priority order for conducting PHAs. In PETRO-SAFE Conference, Houston, TX, 1995; pp Chemical Facility Antiterrorism Standards Regulations. 10. EPA; US

15 References cont d 11. EPA, U. LandView 6, Study, K., A real-life example of choosing an inherently safer process option. Journal of Hazardous Materials 2007, 142, (3), CCPS, Inherently safer chemical processes: A life cycle approach. American Institute of Chemical Engineers: New York, Etowa, C. B.; Amyotte, P. R.; Pegg, M. J.; Khan, F. I., Quantification of inherent safety aspects of the Dow indices. Journal of Loss Prevention in the Process Industries 2002, 15, Methyl Isocyanate Material Safety Data Sheet. Available online at: Rensi, T. A. Multistage process for making methylcarbamates , Lapkin, M. Reducing the storage of Methyl Isocyanate at Rhone-Poulenc's facility in Institute, West Virginia;