process hazards reviews and regulations

Chapter 24Health, Safety, and Environment

NMSU Chemical EngineeringCh E 452

Why Worry about Safety?38 Year DuPont Fatality Summary (1955-92)

0 20 40 60 80 100

explosions

fires

toxic ingestion

chemical burn

suffocation

crushing trauma

process related

non-process related

ca

us

e

number of occurrences

incidentsfatalities

Risk AssessmentActivity OSHA Incident Rate

(injuries & deaths /200,000 h)

Fatal Accident Rate(deaths per 108 h)

Fatality Rate(deaths / person / yr)

Working in Chemical Industry 0.49 4

Staying at Home 3

Working in Steel Industry 1.54 8

Working in Construction 3.88 67

Traveling by Car 57 170 x 10-6

Rock Climbing 4000 40 x 10-6

Smoking (1 pack per day) 5000 x 10-6

Being struck by Lightning0.1 x 10-

6

Regulations and Agencies

• Rules and regulations arise from governmental (OSHA, NIOSH, EPA, DOT, MSHA) and non-governmental agencies (AIChE, API, ASTM, NFPA, etc.)

• Federal government rules are published in the Federal Register (FR) and the Code of Federal Regulations (CFR).

• Important Standards include– OSHA Act and Air Contamination Standard – give exposure limits – Hazard Communication Standard – “worker Right to Know” or

HazCom. Specifies proper labeling of containers and availability of Material Safety Data Sheets (MSDS).

Worker Exposure

• Workers– OSHA

• Permissible Exposure Limit• Threshold Limit Values (ACGIH)

– NIOSH – Recommended Exposure Limits– Short Term Exposure Limit – 15 minute exposure

• Public – EPA – CAA, CWA, SARA– DOT

• MSDS

Time weighted average over 8 hr day

Fires and Explosions

• Combustion - rapid oxidation – At room temp rate usually low– Increases rapidly with temperature– Below auto-ignition temperature – remove heat and

returns to room temperature• Auto-ignition temperature

– above this temperature combustion is sustained when heat source removed.

– Energy to heat small region to above A-I temp is called the ignition energy – very small


• Flammability (or explosive) Limits – LFL (LEL) – min concentration of fuel in oxidant

(usually air) that will support combustion– UFL (UEL) - max concentration of fuel in oxidant

(usually air) that will support combustion– MOC – relates to “inerting”


• Explosion – rapid combustion in which the pressure waves formed propagate the combustion. Waves compresses and heats flammable mixture to its AI temperature.– Deflagraton (< speed of sound)– Detonation (> speed of sound)

• Vapor cloud explosion• BLEVE (boiling-liquid expanding vapor-cloud

explosion – rapid expansion of vapor can cause a massive shock wave)


• Runaway reaction– Insufficient heat removal from exothermic

reaction LOCA (loss of cooling accident)– Use a small or large T for cooling medium?

• Over-pressure– Pressure relief valves– Bursting discs

Inherently Safe Design

• Substitution – avoid• Intensification – use less• Attenuation – less hazardous conditions• Containment – do not let out• Control Leaks – emergency isolation• Survive Leaks – fire protection, etc.

General Duty Clause of the Occupational Safety & Health Act of 1970• Section 5(a)1 requires that every working man and woman

must be provided with a safe and healthful workplace: • “Each employer shall furnish to each of his employees

employment and a place of employment which is free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employee’s”

• Translation: The employer is obligated to protect employees from recognized hazards for which there is not an OSHA standard which applies to the situation or if hazards still exist after compliance with a standard.

How to Read OHSA Regulation Numbering Systeme.g., 29CFR/1910/Subpart H/1910.119/(i)/(2)/(ii)

Title 29 CFR Department of Labor Part 1910 Occupational Safety & Health Subpart H Hazardous Materials Section 1910.119 PSM of Highly Hazardous Chemicals Paragraph (i) Pre-Startup Safety Review Subparagraphs (2) (ii) Safety, operating, maintenance,

emergency procedures...”

Process Safety Management (PSM)(29 CFR 1910.119)Legal Requirements of PSMcontained within subpart H, Hazardous Materialscoverage by this reg is triggered by any of the following:

– having specified threshold quantities of a chemical from the list of PSM regulated chemicals,

– inventory of 10,000 lbs of a flammable liquid or gas, except for hydrocarbon fuels used solely for workplace consumption as a fuel, and flammable liquids stored in atmospheric tanks which are kept below their boiling points without chilling or refrigeration,

– explosives manufacture, or – pyrotechnics manufacture.

29 CFR 1910.119

• Section H contains requirements for preventing or minimizing the consequences of catastrophic releases of toxic, reactive, flammable, or explosive chemicals.

• Standards for dealing with hazards in storage, handling, and processing highly hazardous materials.

• Focus is on all stages of design, development, and operation of a facility. PSM must be communicated to and accepted by all employees of the facility.

Items expressly addressed in 29 CFR 1910.119

(1) Process safety information for many aspects of the process must be developed and maintained, including information regarding or pertaining to

– hazards of chemicals used in the process (MSDS meeting requirements of 29 CFR 1910.1200 (g) ) including; permissible exposure limits, toxicity, physical data, reactivity data, corrosivity data, thermal and chemical stability data, and the hazardous effects of inadvertent mixing;



– the technology of the process, including PFD, process chemistry, maximum intended inventories, safe upper & lower limits of operation (temperature, pressures, flows, compositions), health/safety consequences of deviations from limits;



– the equipment of the process, including; materials of construction, relief system design and design basis, P&IDs, ventilation system, design codes and standards used, material and energy balances, safety systems (interlocks, detection, suppression);



– a process hazard analysis (PHA), including one or more: What-if, Checklist, Hazard and Operability Study (HAZOP), Failure Mode Effect Analysis (FMEA), Fault Tree Analysis (FTA). PHA must address process hazards, previous incidents, engineering and administrative controls and consequences of their failure, siting, human factors, qualitative evaluation of effects of failures on employees. Analysis performed by a team of experts. A system to address the findings put in place. Analysis reviewed every five years. Documentation retained for the life of the process;



– written operating procedures, including: steps for each phase of operations; (initial startup, normal operations, temporary operations, emergency shutdown, emergency operations, normal shutdown, startup following turnaround or emergency shutdown);



– operating limits, including consequences for deviation from limits and steps to correct or avoid deviations,



– safety and health information including hazard information, precautions to prevent explosion, engineering and administrative controls, personal protective equipment, measures taken in the event of an exposure, control of hazardous chemical inventories;



– safety systems and their functions.


2. Operating Procedures will always be readily available 3. Operating Procedures will be periodically reviewed 4. Safe practices will be developed (e.g., lock-out/tag-out) 5. Training will be provided and documented for each employee

involved in operating the process at the time of assignment and on a periodic refresher basis.

6. Regarding contractors, employers shall; evaluate safety performance/programs of a contractor prior to selecting; provide hazards communications to the contractors; provide details of the site emergency action plan; limit contractor access to process area; periodically evaluate contractor performance; maintain illness and injury log for contract employees;


7. Perform a pre-startup safety review for new or modified process facilities prior to the introduction of hazardous chemicals to the process, confirming construction is in accordance with specification; safety, operation, maintenance, & emergency procedures in place; PHR recommendations have been addressed; training is complete

8. Written procedures, describing how mechanical integrity will be maintained for equipment, training on such maintenance, and testing documentation for pressure vessels & storage tanks, piping & valves, relief & vent systems emergency shutdown systems, controls, alarms & interlocks, pumps

9. Hot work permit issuance according to 1910.252(a)


10. Written management of change procedures for process chemicals, technology, equipment and facilities; prior to making change, consider technical basis for proposed change, the impact of change on safety and health, modifications to operating procedures, time required for changes, authorization requirements; prior to startup after change, consideration to retraining of operators, crafts, contractors, update safety data, modify operating procedures

11. Incident investigation 12. Emergency action plan

Process Hazards Reviews• Process Hazards Reviews (PHR) are a systematic,

comprehensive study of a process, performed by a cross-sectional team of employees using recognized analysis methods to:– identify process hazards– identify way in which each hazardous incident may occur– evaluate likelihood of each incident and the consequences

of it occurring– develop practical recommendations to eliminate/control

identified hazards

PHR Team• Chairman

– arranges for process description– assures comprehensive and intensive review– provides documentation and communication

• PHR Resource - individual familiar with PHR procedure, documentation,...

• Remaining Team Composition– operations (hands-on operating experience, previous incidents)– technical (process basis and limits)– maintenance (inspections, equipment history)– specialists (as needed for instruments, mechanical, control, etc.)– consultants (as needed for process safety and fire protection)

PHR Pre-Review Preparation• select review team, define scope of the review• assemble up-to-date process information• all process drawings (current)• relevant past reviews and incident reports• all relevant safety data (MSDSs, regulations,

reports,...)• familiarize team members with process

PHR Review1. Divide process into independent segments (if

possible)2. Identify all hazards and list for each segment3. Select appropriate analysis method for each hazard4. Analyze hazards5. Develop Recommendations6. Compile final report w/ responsibilities/timing on

all recommendations7. Present results for management/operations

approval8. Track and implement recommendations

PHR Methods

• What-If• Checklist• Hazard and Operability Study (HAZOP)• Failure Mode and Effect Analysis (FMEA)• Fault Tree Analysis

What-IF

• based on spontaneously formulated questions by the review team for the specific process under consideration

• unstructured, unbounded, time-driven, based on questioner’s experience

Checklist

• based on an established checklist of items to consider

• based on retrospective experience• no universal checklist exists, relies on finding

appropriate list• concise summary of important items

HAZOP• structured study of specified deviations from design

conditions• model driven and bounded, flexible, good for novel situations• identifies hazards, does not develop solutions• requires trained team leader• timing

– meetings last ~ 2½-3 hours each, not to exceed 2 meetings per week– 1 meeting per P&ID (depending on complexity)– requires a preliminary hazard study & analysis be performed

• requires reasonably firm model (drawings)• assumes good design• looks for deviations from design conditions

HAZOP

• Intention - How process is designed to operate• Deviation - From operating specifications• Cause - How deviation might occur• Consequence - Of deviation with reasonable

causes• Hazard - Consequences that could cause

dangerous situation

HAZOP guide words more of - any relevant physical parameter than there should

be (i.e., more flow, more pressure, more temperature, etc.) less of - opposite of more of none of - none of a system parameter when there should be reverse - the logical opposite (i.e., reverse flow) part of - system composition different from what it should be as well as - more things present than should be (i.e., as

well as a vapor phase when only liquid phase should be present)

other than - total substitution of a fluid or material special - process need other than normal operation (start-up,

shutdown, maintenance, provision for services failures, spare equipment,...)

HAZOP Methoduse guide-words to consider consequences of deviations

GUIDE WORDSmore ofloss ofnone

reversepart of

as well asother

SYSTEMPARAMETERS

flow ratetemperature

pressureviscosity

concentrationduration (time)

deviation fromdesign conditions

cause consequences

HAZOP Guide Word Deviation Matrixmore of less of none of reverse part of as well as other than

flow high flow low flow no flow back flow wrong

conccontaminant

swrong

material

temp high temp

low temp

pres high pressure

low pressure

time too long, too late

too late, too soon

miss a step

backward step

actionmissed

extra actions initiated wrong time

separate matrix can be generated for electrical systems: current, voltage, frequency, phase, start-up/shutdown, interference, power failure…

Deviations Consider

PIPELINE

High Flowpump racing, delivery vessel pressure lost, suction pressurized, scale dislodged, leak in heat exchanger, loss of automated control, operator error

Low Flowpump failure, scaling of delivery, presence of foreign body or sediment, poor suction condition, cavitation, leak in heat exchanger, drain leaking, valve jammed, loss of automated control, operator error

No Flowpump failure, delivery vessel/main overpressurized, gas locking, blockage, presence of foreign body, scale, sediment, suction vessel empty, loss of automated control, operator error, failure of joint, valve, pipe, trap, bursting disk, relief valve

Reverse Flow Pump failure, pump reversed, delivery vessel/main overpressurized, poor isolation, gas locking, surging, back siphoning

High/Low PressureHigh/Low Temperature

boiling, cavitation, freezing, chemical breakdown, flashing, condensation, sedimentation, scaling, foaming, gas release, priming, exploding, imploding, changes in viscosity, density, external fire, weather conditions, hammer

Static Buildup source of ignition, personnel shock

High/Low Concentration changes in proportion of mixture, in water or solvent content

Wrong MaterialContaminations

ingress of air, water, steam, fuel, lubricants, corrosion products, other process materials from high pressure system, leakage through heat exchangers, gas entrainment, spray, mist, etc.

TestingCommissioningMaintenance

vacuum, pressure testing with harmless materialconcentration of reactants, intermediates, abnormal flows, temperatures, pressures, etc.purging, venting, sweetening, drying, washing, access, spares. Should this pipeline be considered for special attention?

VESSELS

High ReactionLow Reaction

frothing, other reaction, runaway reaction, gassing, exothermic, endothermic, enrichment, catalyst

High MixingLow Mixing

agitator failure, vortex, layering, erosion

High LevelLow Level

flooding, pressure surges, corrosion, sludge

BOTH

Failure of Power, Air, Steam, Nitrogen, Water, Fuel, Vacuum, and Vents

consider part and total failures and compound failuresconsider lighting of plant and instrument panels, power for alarms, and local and general failure action of controls

HAZOP Procedure

allguidewordsused

?

select a line or vessel

explain design intention

select guide word

develop meaningful deviation

list causes, consequences, and protections

evaluate need for riskcontrol recommendation

alllines &vessels

done?

YES

YES

done

NO

NO

Table 24.5. HAZOP for the Feed Heater of the Hydrodealkylation (HDA) ProcessProcess Unit: H-101, Feed Heater, Figure 1.3

Intention: To provide feed to the Reactor (Stream 6) at 600ºC.

Guide Word Deviation Cause Consequence Action

No No flow (Stream 4) blockage in line Fluid in H-101 overheats Consider an interlock on fuel gas flow

No O2 in combustion

products

Rich fuel:air mixture Unburned fuel and CO in combustion products

None. O2 analyzer with self-checking circuit controls ratio reliably

O2 analyzer malfunction Potentially rich fuel:air mixture

No flow (Stream 6) Heat tubes burst Explosion Interlock with sudden P drop alarm and shutdown

No benzene in Stream 6

C-101 not working Hydrogen:Toluene ratio off to R-101 and loss of hydrogen to fuel gas

Maintain spare compressor C-101

No fuel gas flow Supply pipe rupture Cold shot to R-101, quenching reaction

Interlock with process shutdown

No flame Momentary loss of fuel gas Explosive mixture Automatic flame detection with re-ignition cycle

4

6

fg air

Failure Mode & Effect Analysis (FEMA)

• based on an investigation of the potential of individual component failures

• component/steps driven• flexible, good for novel situations• requires accurate model and personnel

experienced in FMEA technique

FEMA Objectives• identify component failures which may

cause/contribute to hazardous events• identify component failures which may have multiple

effects on the system (common mode failures)• evaluate adequacy of safeguards, recommend

corrections• identify hazards which require further, possibly

quantitative, analysis to facilitate decisions regarding the extent of improvements required

• document to assure continuity for future review teams

FEMA Concept• assumes “normal mode” is okay• How could this component fail? and

How does failure affect the system?• rating assigned to each failure reflecting severity and

probability of risk 0 = system fails safe or only inconsequential results 1 = reasonable potential for serious injury or small property loss 2 = reasonable potential for a single fatality, multiple serious

injuries or a significant property loss or business interruption 3 = reasonable potential for multiple deaths, large

property/business loss

FEMA Concept1. identify a component2. determine how it can fail3. determine immediate effect of failure (does it cause a process

variable to change, start a problem, defeat a protection system?)4. determine reasonable worst catastrophe that failure could be

involved in5. rate the catastrophe (0-3)6. define failure as inhibitor or enabler7. determine how often failure occurs8. determine how the failure mode is detected9. identify what protections are used to prevent failure10. determine need for further action

FEMA Worksheet

Fault Tree Analysis• logical model and quantification of an identified

major process hazard event

• Advantages– aids decision-making with quantitative evaluation– shows only the failures that lead to the top event– models human failures and process chemistry

• Disadvantages– time consuming– difficult to obtain realistic failure rates– limited scope

FTA Procedure• identify an undesired incident (top event)• model all source causes of top event• assign appropriate failure rates to source

causes• calculate top event frequency• evaluate acceptability of calculated top event

frequenc

FTA Procedure

makedecision:

acceptable?

identify top event

construct the fault tree

analyze qualitatively

analyze quanitatively

accept system

YES

NO

develop improvements

FTA Nomenclature

FTA Construction• select the TOP EVENT• list all necessary, immediate and sufficient causes

– necessary - show all required conditions– immediate - show direct causes, not jumping ahead– sufficient - show only required causes, no extras

• define cause types as system, basis source, or normal source cause

• select gate type• place causes under gate and connect causes to gate

with lines• repeat for every subevent until no subevents remain

Reduce TOP EVENT Frequency• additional safety devices: rupture discs, relief

valves, interlocks• improved design: fail safe or redundant

systems• increased testing frequency: instruments,

mechanical devices• additional warnings: instruments, alarms• improved operating procedures, training,

ergonomics,...

PHR Method Selection Decision

Tree

process hazards reviews and regulations

Documents

process safety information

process safety management

temperature combustion

occupational safety

small fires

section h

permissible exposure

subpart h section