CH 09 703 SAFETY

ENGINEERING IN PROCESS

PLANTS

MODULE II Manilal A M

Dept. of ChE, Govt Engg College Thrissur

CHEMICAL HAZARDS CLASSIFICATION Hazardous chemicals are those that, following

worker exposure, can have an adverse effect on

health.

Major Chemical hazards are classified into

Fire hazard

Hazard due to explosion

Hazard due to toxic chemicals

Radiation hazard

From the escape of process materials which may be inherently dangerous (eg. flammable or toxic) and/or present at high pressures and high or low temperatures.

Large and sudden escapes may cause explosions, toxic clouds and pollution whose effects extend far beyond the works perimeter.

Small and persistent escapes may lead to chronic ill-health and environmental pollution.

HAZARDOUS CHEMICALS

Characteristics which make a substance

hazardous :

Flammability

Explosivity

Toxicity

Reactivity

Corrosivity

Radio activity

HAZARDS DUE TO FIRE

Fire hazards are an important concern. There are two

main kinds of fire hazard. One is that from very

flammable materials, which may give rise quickly to a

dangerous fire or explosion. The other is that from fires

in buildings, which may trap people by the spread of

fire or smoke.

The thermal radiation intensity and the time duration

of fires often are used to estimate injury (severity of

burns) and damage due to a fire.

Effect of fire : Skin burns due to thermal radiation

Human skin can withstand a heat radiation intensity of 10 kW/m2 for approximately 5 seconds and that of 30 kW/m2 for less than 0.4 seconds before pain is felt.

HAZARD DUE TO EXPLOSION

We define an explosion as an event leading to a rapid

increase of pressure. This pressure increase can be

caused by: nuclear reactions, loss of containment in

high pressure vessels, high explosives, metal water

vapour explosions, run-a-way reactions, combustion of

dust, mist or gas (incl. vapours) in air or in other

oxidisers.

Result in a pressure wave.

Damage to materials and property

Explosives industry

Explosions of industrial chemicals outside the

explosives industry.

EXPLOSION

GAS EXPLOSIONS

gas explosion Is a process where combustion of a

premixed gas cloud, i.e. fuel-air or fuel-oxidiser, is

causing rapid increase of pressure. Gas explosions can

occur inside process equipment or pipes, in buildings or

offshore modules, in open process areas or in unconfined

areas.

The consequences of a gas explosion will depend on the

environment in which the gas cloud is contained or which

the gas cloud engulfs. Therefore it has been common to

classify a gas explosion from the environment where the

explosion takes place: i) Confined Gas Explosions within

vessels, pipes, channels or tunnels. ii) Partly Confined

Gas Explosions in a compartment, buildings or off-shore

modules and iii) Unconfined Gas Explosions in process

plants and other unconfined areas.

CHEMICAL EXPOSURES

Sources of Exposure :

Periodic emissions

They arise from the need to open or enter the ‘system’

occasionally, for example, during sampling, cleaning,

batch additions, line breaking etc. Periodic emissions

tend to be large and include both anticipated events

and unplanned releases, in which human error may

be a factor.

Fugitive emissions

Small but continuous escapes from normally closed

sources. 15-20 % of total volatile organic chemical

(VOC) emissions are fugitive. They occur from

dynamic seals such as valve stems and pump or

agitator shafts and from static seals such as flange

gaskets.

CLASSIFICATION OF ATMOSPHERIC

CONTAMINANTS

Carcinogenic

A substance which if it is inhaled or ingested or if it

penetrates the skin may induce cancer in human beings

or increase its incidence.

Teratogenic

A substance which if it is inhaled or ingested or if it

penetrates the skin may involve a risk of subsequent

non-hereditable birth defects in offspring.

Mutagenic

A substance which if it is inhaled or ingested or if it

penetrates the skin may involve a risk of hereditable

genetic defects.

TLV CONTAMINATION REDUCTION OR

REMOVAL METHODS

For the control of air born substances in the work

environment some occupational exposure limits are

fixed. They are the maximum concentrations in air of

the substances which should not be exceeded in the

breathing zone of workers.

The most commonly used Threshold limit values

(TLVs) are

TLV-TWA (Time weighted average)

TLV-STEL (Short term exposure limit)

TLV-c (ceiling )

The Threshold Limit Value - Time Weighted

Average (TLV-TWA) : Time-weighted average

concentration for a normal 8-hour working day and a

40-hour working week, to which nearly all workers may

be repeatedly exposed day after day, without adverse

effect

The Threshold Limit Value - Short Term

Exposure Limit (TLV-STEL) is defined as a 15-

minute, time-weighted average which should not be

exceeded at any time. During a working day, even if the

8-hour time-weighted average is within the TLV

RELEASE OF HAZARDOUS MATERIALS

Toxic releases may consist of continuous releases or

instantaneous emissions. Continuous releases usually involve

low levels of toxic emissions, which are regularly monitored

and/or controlled. Such releases include continuous stack

emissions and open or aerated chemical processes in which

certain volatile compounds are allowed to be stripped off into

the atmosphere through aeration or agitation.

Greater concern is warranted for the case of an instantaneous

release, which is usually the result of an uncontrolled process.

Most of these incidents are the result of a highway or railway

accident or a fire, windstorm, or other natural accident.

However, the cause can sometimes be linked to the breakdown

of normal safeguards in plants, factories, mines, or chemical

storage facilities. Whatever the cause, the result is often a

significant potential threat to life, property, and/or file

environment.

Continuous versus Instantaneous Releases

RADIATION HAZARD

Radioactive materials that decay spontaneously produce

ionizing radiation, which has sufficient energy to strip

away electrons from atoms (creating two charged ions) or

to break some chemical bonds.

Any living tissue in the human body can be damaged by

ionizing radiation in a unique manner. The body attempts

to repair the damage, but sometimes the damage is of a

nature that cannot be repaired or it is too severe or

widespread to be repaired.

Also mistakes made in the natural repair process can lead

to cancerous cells. The most common forms of ionizing

radiation are alpha and beta particles, or gamma and X-

rays.

RADIATION HAZARD In general, the amount and duration of radiation

exposure affects the severity or type of health effect.

There are two broad categories of health effects:

stochastic and non-stochastic.

Stochastic Health Effects

Stochastic effects are associated with long-term, low-level

(chronic) exposure to radiation. Increased levels of

exposure make these health effects more likely to occur,

but do not influence the type or severity of the effect.

Cancer is considered by most people the primary health

effect from radiation exposure. Damage occurring at the

cellular or molecular level, can disrupt the control

processes, permitting the uncontrolled growth of cells

cancer This is why ionizing radiation's ability to break

chemical bonds in atoms and molecules makes it such a

potent carcinogen.

Radiation can cause changes in DNA, the "blueprints"

that ensure cell repair and replacement produces a

perfect copy of the original cell. Changes in DNA are

called mutations.

Sometimes the body fails to repair these mutations or

even creates mutations during repair. The mutations

can be teratogenic or genetic. Teratogenic mutations are

caused by exposure of the fetus in the uterus and affect

only the individual who was exposed. Genetic mutations

are passed on to offspring.

Non-Stochastic Health Effects

Non-stochastic effects appear in cases of exposure to

high levels of radiation, and become more severe as the

exposure increases. Short-term, high-level exposure is

referred to as 'acute' exposure.

Many non-cancerous health effects of radiation are

non-stochastic. Unlike cancer, health effects from

'acute' exposure to radiation usually appear quickly.

Acute health effects include burns and radiation

sickness. Radiation sickness is also called 'radiation

poisoning.' It can cause premature aging or even

death. If the dose is fatal, death usually occurs within

two months.

The symptoms of radiation sickness include: nausea,

weakness, hair loss, skin burns or diminished organ

function.

Medical patients receiving radiation treatments often

experience acute effects, because they are receiving

relatively high "bursts" of radiation during treatment.

REDUCTION OF PROCESS HAZARDS BY PLANT

CONDITION MONITORING.

The general principle of condition monitoring involves the

selection of some appropriate indicator of the machine

condition, which can be measured at ntervals.

This measurement is recorded and is then usually plotted

on a graph, against time in service, to indicate whether

deterioration is occurring.

The object of the condition monitoring activity is to

achieve a lead time or advanced warning of failure to

enable the machine or plant to be taken out of service in a

planned manner .

Failures in service can then be eliminated and the

maintenance operation can also be much more efficient,

because the necessary spares and skilled labour can be

standing by to do the job.

The principles of condition monitoring

There are five basic methods used at present for

monitoring the condition of plant and machinery and

these are: -

1. Visual monitoring.

2. Vibration monitoring.

3. Wear monitoring.

4. Performance monitoring.

5. Corrosion monitoring.

All these methods really involve an extension of long

established machine minding practice by the application of

modern technology.

ADVANTAGES OF CONDITION MONITORING

THE GENERAL APPLICATION OF MONITORING METHODS TO

THE DETECTION AND DEFINITION OF MACHINE PROBLEMS