Chemical Process Safety Slides for Final Exam

yellow diamond

reactivity

LOPA is limited to what?

to evaluating a single cause consequence pair as scenario

puff model

transient. sudden discharge of a finite quantity of material. function of position and time

deflagration

a fire or reaction which propagates at below the speed of sound

chronic hazard

a hazard whose effects manifest themselves over a long period of time

leading indicator

a measure preceding or indicating a future event used to drive and measure activities carried out to prevent and control injury. proactive in nature and report what employees are doing on a regular basis

detonation

a reaction where the reaction front travels at greater than the speed of sound. because the reaction happens faster than the speed of sound, the amount of energy that can be scrubbed off by expansion is limited. this causes a much higher pressure and temperature behind the blast wave increasing the blast efficiency

3 types of industrial hygiene control

administrative controls, engineering controls, personal protective equipment

alk

alkali

adiabatic temperature rise

allows one to determine if a loss of cooling control will raise the temperature enough to trigger a secondary reaction

confined space entry

an OSHA requirement. required permit at most refineries, chemical plants, and many other industries

effective dose ED50

dose which produces measureable but reversible effects in 50% of population

dust pentagon

dust explosions can be prevented by removing any side. ignition source, dispersion, oxygen, fuel, confinement

blue diamond

health hazard

response of reaction to temperature

higher T makes all reactions go faster. different reactions respond to temperature changes differently according to arrhenius law

facility siting

identify, evaluate, and manage the potential hazards and risks to onsite and offsite occupied areas from potential fire, explosion and toxic material release events. protect personnel in occupied site buildings from the potential serious effects of releases. protect the public in offsite but nearby buildings from the same

IDLH

immediately dangerous to life and health

inherently safer design strategies

minimize, substitute, moderate, simplify

disadvantages to rupture discs

dont reclose after relief, burst pressure cannot be tested, require periodic replacement, greater sensitivity to mechanical damage, greater sensitivity to temperature

toxic dose TD50

dose which produces irreversible harmful effects in 50% of population

what reduces ground level concentration?

raising height of release point

3 key actions in reducing risk

1. identifying and classifying a risk level 2. identifying ways to decrease the risk 3. quantify the effects of the risk reduction efforts

divisions

I is flammable concentrations are normally present II is flammable concentrations are present only under abnormal situations

classes

I is locations with flammable gases or vapors II is locations with flammable dusts

PSM management

a comprehensive set of policies, procedures, and practices to ensure barriers are in place to mitigate the chance of a release of chemicals

process safety

a discipline that is focused on prevention and preparation of releases of chemicals

grounding

connecting equipment to ground

hazards are relatively ranked into what?

consequence categories based on a few available parameters

cor

corrosive

risk

coupling of the consequence and frequency of a scenario

buckling pins

designed to be a non reclosing pressure relief device similar to a rupture disc

modeling of consequences

dispersion modeling, explosion modeling, and toxic modeling are usually not done at the LOPA stage

conditions for dust explosion to occur

dust must be combustible, must have particle size distribution that allows propagation of flame, atmosphere in which dust is dispersed must contain sufficient oxidant

bonding

electrically connecting two equipment pieces

causes of chatter

excessive inlet pressure drop, excessive built up back pressure, oversized valve, valve handling widely differing rates

red diamond

fire hazard

fire triangle

fires can be prevented by removing any single leg. oxidant, fuel, ignition source

assumptions for gas flow through hole

fluid is compressible, friction can be expressed as discharge coefficient, expansion is adiabatic, change in height is insignificant

assumptions for liquid flow through hole

fluid is non compressible, friction can be expressed as discharge coefficient, pressure is constant, change in liquid height is zero

reaction calorimetry

for scale up the heat flow produced by a given volume of reaction mass cannot exceed the heat removal capacity of the reactor if temperature control is to be maintained

heat transfer

for the reactor to stay isothermal, heat transfer q must equal the heat flow produced by the reaction plus the agitator power

static electricity

formation mechanisms are rubbing, falling, moving, flowing, separation.

qualitative

frequency is often expressed as likelihood. consequence may be expressed as in general terms (major, moderate, minor)

GHS

globally harmonized system. requires chemical manufactures to determine the hazards associated with their chemicals labels be utilized, material safety data sheets be provided

HAZOP

hazard and operability studies

entry route for toxicants

ingestion, inhalation, injection, dermal absorption

LOPA is commonly used in industry

is a risk assessment and mitigation tool, is a semi quantitative tool, is to be used with PHAs. is not a replacement for PHA

lethal dose LD50

kills 50% of populaion

LOPA

layers of protection analysis. a semi quantitative tool used to determine risk

LOC

limiting oxygen concentration. oxygen concentration below which combustion is not possible, with any fuel mixture. lowest concentration of oxygen which will form a flammable mixture

types of release

liquid/gas flow through hole, liquid/gas flow through open pipe, flashing liquid, liquid evaporation, gasket failures

control of hazardous energy

lockout tagout is an OSHA standard but not required. requires isolation of electrical and other hazardous energy sources before working on equipment

LFL

lower flammability limit. below LFL, mixture will not burn

MAWP

maximum allowable working pressure. maximum design pressure at the top of a vessel for a designated temperature

MTSR

maximum temperature (adiabatic) of the synthetic reaction. the temperature the reaction would reach in the absence of cooling

lagging indicator

measure a company's incidents in the form of past accident statistics. tell you how many people got hurt and how badly

HAZOP advantages

meets regulatory requirements, plant operates better, less down time, product quality improved, employees are happier

MEC

minimum explosible concentration. the minimum concentration of an explosible dust cloud that is capable of propagating a deflagration through a uniform mixture of dust and air under the specified conditions

MIE

minimum ignition energies. energy required to ignite a flammable mixture

advantages to conventional spring loaded valve

most reliable type if properly sized and operated. versatile

secondary explosions

most severe and destructive. caused when the powder/dust on the floor and beams is jarred loose and thrown into one large dust cloud and ignited by the fireball from primary reaction

NEP

national emphasis program on combustible dusts

HAZOP guidewords

no, more, less, as well as, part of, reverse, other than, sooner than

propagating explosions

normally starts as a primary explosion in a piece of equipment and propagates to all of the interconnected equipment

what is a confined space?

not designed for human occupancy. large enough to enter and preform work. limited means of entry/exit.

process/reaction hazard testing purpose

obtain data for emergency relief system design, evaluate thermal stability of a material, obtain pt data for process systems, detect and measure gas generation and rate of pressure rise

oxy

oxidizer

factors influencing sensitivity and explosion characteristics of dust clouds

particle size, surface area, chemical composition, moisture content, initial pressure temperature of the gas phase, distribution of particle sizes, degree of dispersion

inherently safer

permanently and inseparably reduces or eliminates process hazards. avoidance of hazards rather than their control

hot work permits cont

plant areas with combustible vapors and dusts control ignition sources. hot work helps prevent fires and explosions. electrical area classifications and explosion proof electrical equipment also eliminate ignition sources. hot work permits control intermittent ignition sources needed for maintenance or other special operations

set pressure

pressure at which the relief device begins to open

overpressure

pressure increase over set pressure during relieving

pressure relief devices

pressure relief valves, rupture disks, buckling pins

combustible dust explosions

primary explosions, propagating explosions, secondary explosions

PSM

process safety management. divided into 14 elements

general classification risk approaches

qualitative, semi-quantitative, quantitative (QRA)

advantages to rupture discs

reduced fugitive emissions, no simmering or leakage prior to bursting, protect against rapid pressure rise caused by heat exchanger tube ruptures, less expensive, less tendency to foul or plug

what do source models provide?

release rate, total amount released, state of material

advantages to pilot operated valve

relieving pressure is not affected by backpressure, can operate at up to 98% of set pressure, less susceptible to chatter

advantages to bellows valve

relieving pressure not affected by back pressure. can handle higher built up back pressure. protects spring from corrosion

hot work permits

required by OSHA PSM. a key is to make sure there are no flammable hydrocarbons in the hot work area or introduced into the area by the people doing the work

isolation procedures

shutdown/shutoff the source of hazardous energy. remove any residual energy (pressure, potential, electrical, depressure) lock electrical breakers in the closed position, remove pneumatic air or electricity that allows automatic valves to operate, lock valves in their closed position, place a tag on each lock signed by the person isolating, try to start any electrically locked equipment

types of fires

smoldering fires, flash fires, spreading fires

acute hazard

something which is hazardous immediately and generally in high concentration

plume model

steady state charge of material. function of position

two types of backpressure

superimposed and built up

disadvantages to pilot operated valve

susceptible to plugging, limited chemical and high temperature use, vapor condensation and liquid accumulation above the piston may cause problems

flash point

temperature above which a liquid produces enough vapor to form an ignitable mixture with air or the lowest temperature where a non propagating fire will occur above a pool of liquid

HAZOP process parameters

temperature, pressure, flow, level, concentration, agitation, reaction, start, stop, power, component

Pmax

the maximum pressure developed in a contained deflagration of an optimum mixture

where is the highest concentration in dispersion

the point of release

backpressure

the pressure downstream of the relief device during the relieving process

accumulation

the pressure increase over the MAWP of the vessel during the relief process

chatter

the rapid alternating opening and closing of a PR valve

TLV

threshold limit value. max concentration which TWA- limit over 8hr STEL-limit in any 15 min C- instantaneous limit

HAZOP disadvantages

time, people and effort, information management challenges

UFL

upper flammability limit. above UFL mixture will not burn

w

use no water

quantitative evaluation of frequencies from fault trees and event trees

usually not done at this LOPA stage

how can a cloud be better dispersed?

wind and less stable atmosphere