Safety Practices in Chemical and Nuclear Industries - …nptel.ac.in/courses/103106071/lec3.pdf ·...

Safety Practices in Chemical and Nuclear Industries

Dr. Raghuram Chetty Department of Chemical Engineering

Indian Institute of Technology Madras Chennai- 600 036.

Toxic Substance and Confined Spaces

Lecture 3

Contents

Toxic substances Definition Entry Points for Toxic Agents Effects of Toxic Substance

Relationship of Doses and Responses

Threshold Limiting Values Exposure Thresholds Airborne Contaminants

Confined Spaces Hazards

Prevention and Control

Toxicology

Because of the quantity and variety of chemicals used by the chemical process industries, we must have knowledge on

The way toxicants enter biological organism

The way toxicants are eliminated from biological organisms

The effects of toxicants on biological organisms

Method to prevent or reduce entry of toxicants

Toxicology

Long ago, toxicology was defined as the science of poisons. Paracelsus, an early investigator of toxicology during 1500s stated the problem: “All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy”. Harmless substance, such as water, can become fatal if delivered to the biological organisms in large enough doses.

A fundamental principle of toxicology is

‘There are no harmless substances, only harmless ways of using substances’.

Toxicology

Toxicology can be defined as the qualitative and quantitative study of the adverse effects of toxicants on biological organisms. A toxicant can be a chemical or physical agents, including dusts, fibres, noise and radiation.

The toxicity of a chemical or physical agent is a property of the agent describing its effect on biological organisms. Toxic hazard is the likelihood of damage to biological organisms based on exposure of usage.

The toxic hazard of a substances can be reduced by appropriate industrial techniques. The toxicity, however, cannot be changed.

Toxic Substance

A toxic substance is one that has a negative effect on the health of a person or animal.

Toxic effects are a function of several factors, including:

Properties of the substances

Amount of the dose

Level of exposure

Route of entry

Resistance of the individual to the substance

Response can vary widely and might be as little as a cough or mild respiratory irritation or as serious as unconsciousness and death.

Entry Points for Toxic Agents

The development of preventive measures to protect against the hazards associated with industrial hygiene requires first knowing how toxic agents enter the body.

The most common routes of entry for toxic agents are:

Inhalation Entry organ: Mouth or nose

Adsorption Entry organ: Skin

Ingestion Entry organ: Mouth or stomach (not a major industrial concern)

Injection Entry organ: Cuts in skin

Inhalation

Airborne toxic substances such as gases, vapors, dust, smoke fume, aerosols, and mists can be inhaled and pass through the nose, throat, bronchial tubes, and lungs to enter the bloodstream.

The amount of a toxic substance that can be inhaled depends on the

Concentration of the substances

Duration of the exposure

Breathing volume. Image courtesy: Google Images

Adsorption Passage through the skin and into the

bloodstream

Organic lead compounds, nitro compounds, organic phosphate pesticides, TNT, cyanides, aromatic amines, amides, and phenols.

With many substances, the rate of absorption and in turn, the hazard levels increase in a warm environment.

Factors affecting absorption rate

Molecular size

Degree of ionization

Lipid solubility

Aqueous solubility Image courtesy: Google Images

Entry Routes & Method for Control

Entry Route Entry Organ Method of Control

Ingestion Mouth Enforcement of rules on eating and drinking

Inhalation Mouth or nose Ventilation, respirators, hoods, and other PPE

Injection Cuts in skin Proper protective clothing

Absorption (dermal) Skin Proper protective

clothing

Effects of Toxic Substance

The effects of toxic substance vary widely, as do the substances themselves. However, all of the various effects and exposure times can be categorised as being either acute or chronic.

Acute effects/exposure involves a sudden dose of a highly concentrated substance. They are usually the result of an accident (a spill or damage to a pipe line) that results in an immediate health problem ranging from irritation to death.


Acute effect/exposure are

Sudden

Severe

Typically involve just one incident

Causes immediate health problems

Chronic effects/exposures involve limited continual exposure over time. Consequently, the associated health problems develop slowly.

The characteristics of chronic effects/exposure are:

Continual exposure over time

Limited concentrations of toxic substances

Progressive accumulation of toxic substance in body

Little of no awareness of exposures.


When a toxic substance enters the body, It eventually affects one or more body organs. Part of the liver’s function is to collect such substances, convert them to non-toxics and send them to the kidneys for elimination in the urine


Chronic effects/exposures…

However when the dose is more than the liver can handle, toxics move on to the organs, producing a variety of different effects.

The organs that are effected by toxic substances are the blood, kidneys, heart, brain, central nervous system, skin, liver, lungs and eyes.


Various responses to Toxicants

Effects that are irreversible

Carcinogen causes cancer

Mutagen causes chromosome damage

Reproductive hazard causes damage to reproductive system

Teratogen causes birth defects

Various responses to Toxicants

Effects that may or may not be reversible

Dermatotoxic affects skin

Hemotoxic affects blood

Hepatotoxic affects liver

Nephrotoxic affects kidney

Neurotoxic affects nervous system

Pulmonotoxic affect lungs

Carcinogens

A carcinogens is any substance, that can cause a malignant tumour or a neoplastic growth.

Medical researchers are not sure exactly how certain chemicals cause cancer. However, there are a number of toxic substances that are either known or, are strongly suspected to be carcinogens.

Examples: coal tar, pitch, anthracene oil, soot, lamp black, lignite, asphalt, bitumen waxes, paraffin oils, arsenic, chromium, nickel compounds, berylium, cobalt, benzene, and various paints, dyes, pesticides and enamels.

Asbestos Hazards

More than 70% of the commercial buildings in use today contain asbestos in some form -because of its useful characteristics such as fire resistance, heat resistance, mechanical strength and flexibility.

In mid-1970’s medical research tied asbestos to respiratory cancer, scarring of lungs, etc and it was finally banned by EPA in 1989.

Asbestos Hazards

When asbestos becomes crumbly, it releases fibers into the air that are dangerous when inhaled. Asbestos can be released into the air if it is disturbed during renovation or as a result of vandalism.

Permissible exposure limit (PEL) is 0.2 fibers per cm3 of air for an 8 hour time weighted average.

Toxic substances & the organs they endanger

Blood Kidneys Heart Brain

Benzene Carbon monoxide

Arsenic Aniline Toluene

Mercury Chloroform

Aniline Lead Mercury Benzene

Manganese Acetaldehyde

Eyes Skin Lungs Liver

Cresol Acrolein

Benzyl chloride Butyl alcohol

Nickel Phenol

Trichloroethylene

Asbestos Chromium

Hydrogen sulfide Mica

Nitrogen dioxide

Chloroform Carbon-

tetrachloride Toluene

Some of the widely used toxic substances and the organs they endanger

How toxicants are eliminated?

Toxicants are eliminated or rendered inactive by the following routes:

Excretion: through the kidney, liver, lungs or other organs.

Detoxification: by changing the chemical into something less harmful by biotransformation.

Storage: in the fatty tissue.

How toxicants are eliminated?

Toxicants that are ingested into the digestive tract are frequently excreted by the liver. In general, chemical compounds with molecular weights >300 are excreted by the liver into bile. Compounds with lower molecular weights enter the bloodstream and are excreted by the kidneys.

Animal Testing How is toxicity tested?

Most toxicological data is collected using small rodents e.g. rats, mice, Guinea pigs, as surrogates for human beings.

There are numerous advantages to using such animals. They are small and relatively easy to maintain in good health in the laboratory. With a life expectancy of typically 2 years, one can see the effect of a lifetime of exposure in a relatively short time.

Designing toxicological experiments

Manner of dosing

There are several pathways for dosing. Most commonly, the test substance is added to the food or water, placed directly into the stomach by gavage, injected into a vein, coated onto the skin, or added to the atmosphere the animal breathes.

The final toxicity values obtained usually differ according to the path of entry into the body.


Manner of dosing

The chosen path reflects the following concerns. What will be the manner of exposure of workers in the

plant? It should be replicated as nearly as possible in the testing. For e.g. a solvent to be used for degreasing parts may make contact with the skin of the worker or its vapors may be inhaled, but it is highly unlikely that the worker would ever swallow any. Testing should concentrate on exposure to the skin and lungs.

The actual design of the experiment depends on how the dose is to be administered and what responses are to be studied.


Manner of dosing

Length of testing time

When the dosing is for a limited time - acute

The animal’s lifetime study - chronic

Variability among animals

The toxicity of a compound is not a constant term for all animals. Differences are sometimes displayed between animals of even very closely related species.

Relationship of doses and responses

Safety and health professionals are interested in predictability, when it comes to toxic substances.

How much of a given substance is too much?

What effect will a given does of a given substance produce?

Relationship of doses and responses

These types of question concern dose-response relationships.

A dose of a toxic substance can be expressed in a number of different ways depending on the characteristics of the substance, e.g.

amount per unit of body weight

amount per body surface area

Extrapolating Animal Data to Humans

In spite of all the advantages, using mice or rats to predict toxicity to human involves many risks.

The difference in size between human and small rodents is a major problem. The observation that 1 mg of a compound makes a white rat ill dose not mean that the same amount of would make a human ill.

Extrapolating Animal Data to Humans

Most commonly doses are listed in milligrams of compound given the animal per kilogram of animal body weight. Thus the dose of 1mg per 250-g rat is a dose rate of 4mg/kg.

One assumes that the same dose rate should affect the human, and that 280 mg would have roughly the same effect on a 70-kg human. Because of difference between rats and humans this is almost certainly not exactly true, but it does provide a useful first approximation of toxicity to humans.

Example

25 mg of a narcotic substance under study causes a 200 g rat to sleep for 1 hour. What is this dose rate in mg/kg?

200 g 25 mg

1 kg 125 mg

1 kg 1000 g

= x

Example

As a first approximation, what dose would be needed to produce the same effect on an 80-kg human?

1 kg

125 mg x 80 kg = 10,000 mg x = 10.0 g

1000 mg

1 g

Example

What dose would be predicted to put a 32 kg dog to sleep?

1 kg

125 mg 1000 mg

1 g x 32 kg = 4,000 mg x = 4.0 g

Doses

Three important concepts to understand relating to doses are:

Dose Threshold

Lethal Dose

Lethal Concentration

Dose Threshold

The minimum dose required to produce a measurable effect.

Of course, the threshold is different for different substances.

In animal tests, thresholds are established using methods such as:

Observing pathological changes in body tissues

Observing growth rates (are they normal or retard)

Measuring the level of food intake (has there been a loss of appetite)

Weighing organs to establish body weight to organ weight ratios

Lethal Dose

Lethal dose of a given substance is the dose that is highly likely to cause death. Such doses are established through experiments on animals

When lethal doses of a given substance are established, they are typically accompanied by information that is of value to medical professionals and industrial hygienists.

Such information includes: the type of animal used in establishing the lethal dose

how was the dose administered

the duration of the dose.

Lethal doses do not apply to inhaled substances.

Lethal Dose That all animals, no matter how carefully

selected, do not respond identically to a given dosage now becomes a problem in communications of the findings.

Do we select the lowest dose that caused a susceptible animal to die, the highest necessary to kill the most resistant animal, or an average dose?

To resolve this, the fist step is to prepare a dose-response curve from the data.

Percentage mortality is plotted against Log dose in mg/kg. This is also called as Probit Analysis (Probit = Probability unit).

Lethal Dose

At the centre of this curve is found the dose that is estimated to be fatal to half the recipient animals. This dose, the acute LD50 is predicted to be lethal to 50% of the animals, and is the most common value used to describe the relative toxicity of a compound.

Once the curve is established it is possible to describe other measures of toxicity such as LD5 (dose lethal to 5% of animal sample) or LD95.

Toxicity class and LD50 values Toxicity Rating

Descriptive Term

LD50 wt/kg (single oral

dose in Rats)

4-hr inhalation LC50 in Rats

(ppm)

Extrapolated Dose (g) for 70-kg

Human

1 2 3 4 5 6

Extremely toxic Highly toxic Moderately toxic Slightly toxic Practically nontoxic Relatively harmless

<1 mg 1-50 mg

50-500 mg 0.5-5 g 5-15 g >15g

<10 10-100

100-1,000 1,000- 10,000

10,000-100,000 >100,000

<0.07 0.07-3.5 3.5-35 35-350

350-1000 >1,000

Compounds LD50 (mg/kg, rats, oral)

Glycerol Ethanol Ethylene glycol Acrylic acid Hydroquinone Acrylamide Acrylonitrile Nicotine Dioxin

25,200 10,300 8,500 2,600 320 170 93 1 0.001 Dose-response curve for ethyl

alcohol

Lethal Concentration A lethal concentration of an inhaled substance is the

concentration that is highly likely to result in death.

With inhaled substances, the duration of exposure is critical because the amount inhaled increases with every unprotected breath.

In this case, the dose taken by the animal dose not have to be adjusted to the size of the animal (e.g. when intake is through lungs), the standards are based on the concentrations of the substance in the environment of the animal. The toxicity is expressed as the LC50, or concentration lethal to 50% of the test group.

The units in this case are usually either parts per million (ppm) or mg/m³ of air.

Threshold Limiting Value

The Threshold Limit Values (TLV) for chemical substances is defined as a concentration in air, typically for inhalation or skin exposure.

TLV refer to airborne concentrations of substances and represent conditions under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse health effect.

Its units are in parts per million parts of air (ppm) for gases and mg/m³ for particulates such as dust, smoke and mist.

Threshold limits are based on the best available information from industrial experience, form experimental human and animal studies, and when possible from a combination of the three.


Substance TLV (ppm) TLV (mg/m3) Acetic Acid 10 25

Acetone 750 1188 Ammonia 25 17 Benzene 1 1.6

Carbon Dioxide 5000 9000 Chloroform 10 49

Ethyl Alcohol 1000 1880 Formic Acid 5 9.4 Nitric Acid 2 5.2 Toluene 50 188

TLV’s of Some Common Chemicals


TLV (also called exposure threshold) is a specified limit on the concentration of selected chemicals. Exposure to these chemicals that exceed the threshold may be hazardous to a worker’s health.

Three types of TLVs for chemical substances are (1) time-weighted average, (2) short-term exposure limit, and (3) exposure ceiling.

The Time Weighted Average (TLV-TWA) is the average concentration of a given substance to which employees may be safely exposed over an 8 hour work day or a 40 hour work week. Workers can be exposed without adverse effect.


Short-Term Exposure Limit (TLV-STEL) is the maximum concentration of a given substance to which employees may be safely exposed for up to 15 minutes without suffering irritation, chronic tissue change, or narcosis to a degree sufficient to increase the potential for accidental injury.

The exposure Ceiling (TLV-C) refers to the concentration level of a given substance that should not be exceeded at any point during an exposure period.

TLV-Time Weighted Average

Recommended maximum exposures are expressed on the basis of time-weight averaged (TLV-TWA).

Calculations of a TLV-TWA assumes an 8-hr day and 40-hr week. The exposure levels of the compounds are measured in regular intervals.

TLV-Time Weighted Average

The TWA exposure is calculated by multiplying the concentration of compound in each analysis by the length of time of exposure to that level. These are summed and divided by the total time to produce an average exposure level.

Evaluating Exposure to Volatile Toxicants

A direct method for determining worker exposure is by continuously monitoring the air concentration of toxicants on-line in a work environment. For continuous concentration data C(t) the TWA (time-weighted averaged) concentration is computed using the equation:

where C(t) is the concentration (in ppm or mg/m3) of the chemical in air

tw is the worker shift time in hours

∫ tw

0

TWA = 1

8 C(t) dt


The integral is always divided by 8 hrs, independent of the length of time actually worked in the shift. Thus, if a worker is exposed for 12 hrs to a concentration of chemical equal to the TLV-TWA, then the TLV-TWA has been exceeded, because the computation is normalised to 8 hrs.

Continuous monitoring is not the usual situation because most facilities do not have the necessary equipment available.


The more usual case is for intermittent samples to be obtained, representing worker exposures at fixed points in time. If we assume that the concentration Ci is fixed (or averaged) over the period of time Ti, the TWA concentration is computed by

TWA = C1T1 + C2T2 +… CnTn / 8 hrs


If more than one chemical is present in the workplace, the combined exposures from multiple toxicants with different TLV-TWA is determined from the equation

where n is the total number of toxicants

Ci is the concentration of chemical i with respect to the other toxicants

(TLV-TWA) is the TLV-TWA for chemical species i.

∑ = Ci

(TLV-TWA)i

n

i = 1

Gas monitors & detectors

Gas Chromatogram

Image courtesy: Google Images

Sample Problem

Given an exposure level of 2 ppm for 10 hr per week, 3 ppm for 20 hr per week and 4 ppm for 10 hr per week, what is the TWA for this exposure?

Exposure (ppm) Time (hr) Product (ppm x hr)

2 10 20

3 20 60

4 10 40

TWA = 120 ppm x hr /40 hr = 3 ppm

40 120

Determine the 8 hrs TWA worker exposure if the worker is exposed to toluene vapour as follows:

Duration of exposure (hr)

Measured concentration

(ppm) 2 1 3

110 330 90

TWA = C1T1 + C2T2 + C3T3 / 8 = 110(2) + 330(1) + 90(3) / 8 = 102.5 ppm

Sample Problem

Because the TLV of toluene is 50 ppm, the worker is overexposed. So additional control measure needs to be developed. On a temporary and immediate basis all employees working in this environment need to wear the appropriate respirators.

Sample Problem

Sample Problem

Air contains 5 ppm of diethylamine (TLV-TWA of 10 ppm), 20 ppm of cyclohexanol (TLV-TWA of 50 ppm) and 10 ppm of propylene oxide (TLV-TWA of 20 ppm). Has the TLV-TWA level been exceeded?

∑ =

Ci

(TLV-TWA)i

n

i = 1

= 5/10 + 20/50 + 10/20 = 1.40

The sum of the fraction for the various components of the mixture are added, and if the total is more than 1, exposure goes beyond acceptable limit.

Because the quantity is greater than 1, the TLV-TWA has been exceeded.

Permitted Exposure Level (PEL)

The difference between TLV and PEL is the agencies from which they come. TLVs are developed by the American Conference of Governmental Industrial Hygienists (ACGIH). PELs are developed by the Occupational Safety and Health Administration (OSHA). They both serve the same purpose and their values are very similar or even identical in many cases

The level of the chemical in the workplace should be monitored, and the level found should be no higher than the permitted exposure level.

Permitted Exposure Level (PEL)

Simple formulas can be used to calculate compliance and safety when PELs are known for all components of the mixture.

A fraction is made of the actual level of a chemical divided by the PEL, where both values must be in the same units. The sum of the fraction for the various components of the mixture are added, and if the total is more than 1, exposure goes beyond acceptable limit.

Airborne Contaminants

It is important to understand the different types of airborne contaminants that may be present in the workplace.

Each type of contaminants has a specific definition that must be understood in order to develop effective safety and health measures to protect against it.


The most common types of airborne contaminates are:

Dusts

Fumes

Smoke

Aerosols

Mists

Gases

Vapours

Dusts Dusts are various types of solid particles that are

produced when a given type of organic or inorganic material is scraped, sawed, ground, drilled, handled, heated, crushed, or otherwise deformed.

The degree of hazard represented by dust depends on the toxicity of the parent material and the size and level of concentration of the particles.


Fumes The most common causes of fumes in the workplace

are such manufacturing processes as welding, heat treating, and metalizing, all of which involve the interaction of intense heat with a parent material.

The heat volatizes portions of the parent material, which then condenses as it comes in contact with cool air. The result of this reaction is the formation of tiny particles that can be inhaled.


Smoke It is the result of the incomplete combustion of

carbonaceous materials. Because combustion is incomplete, tiny soot and/ or carbon particles remain and can be inhaled.


Aerosols Aerosols are liquid or solid particles that are so small

they can remain suspended in air long enough to be transported over a distance. They can be inhaled.

Mists Mists are tiny liquid droplets suspended in air. Mists

are formed in two ways:

when vapours return to a liquid state through condensation,

when the application of sudden force or pressure turns a liquid into particles.


Gases Unlike other airborne contaminants that take the form

of either tiny particles or droplets, gases are formless.

Gasses are actually formless fluids. Gases become particularly hazardous when they fill a confined unventilated space.

The most common sources of gases in an industrial setting are from welding and the exhaust from internal combustion engines.


Vapours Certain materials that are solid or liquid at room

temperature and at normal pressure turn to vapour when heated or exposed to abnormal pressure. Evaporation is the most common process by which a liquid is transformed into a vapour.


Effects of airborne toxics

Airborne toxic substances are also classified according to the type of effect they have on the body. The primary classifications are:

Irritants

Asphyxiant

Narcotics/Anesthetic

For reporting the toxicity of airborne toxicants, no adjustment is necessary for the ratio of animal to human size. One assumes that the rat and human each breath an amount of air that is in proportion to the size. The dose is therefore listed in terms of the concentration in the air, with no reference to animal size.

Irritants Irritants are substances that cause irritation to the

skin, eye and the inner lining of the nose, mouth, throat and upper respiratory tract.

Asphyxiants Asphyxiants are substances that can disrupt breathing

so severely that suffocation results.

Asphyxiants may be simple or chemical in nature.


Simple asphyxiant is an inert gas that dilutes oxygen in the air to the point

that the body cannot take in enough air to satisfy its need for oxygen.

CO2, ethane, helium, hydrogen, methane and nitrogen.

Chemical asphyxiant by chemical interfere with the passage of oxygen into

the blood or the movement of oxygen from lungs to body tissues.

CO, hydrogen cyanide, hydrogen sulfide.

Either way, the end result is suffocation due to insufficient or no oxygenation.


Narcotics/Anesthetic

Are similar in the meaning carefully controlled dosages can inhibit the normal operation of the central nervous system without causing serious or irreversible effects.

This make them particularly valuable in a medical setting.

However if the concentration of the dose is too high, narcotics and anesthetics can cause unconsciousness and even death.

Examples: methyl-ethyl-ketone, acetylene, ether, hydrocarbons and chloroform.


Confined Space Hazards

Confined space means a space that has any of the following characteristics:

limited openings for entry and exit;

unfavorable natural ventilation;

not designed for continuous worker occupancy.

It includes, but is not limited to, boilers, manholes, furnace, pressure vessels, cargo tanks, ballast tanks, sewage-tanks, bins, pits, tunnels, pipes, pump-rooms, compressor rooms, cofferdams, void spaces, duct keels, inter-barrier spaces and engine crankcases.

Confined space e.g. cargo tanks


Confined Space



Atmospheric hazards

Oxygen Deficiency

Oxygen Enriched

Flammable atmosphere

Toxic or Irritating Atmosphere


Physical hazards

Fixed & portable mechanical equipment

Electrically energized conductors

Fluids: Liquids, powders & gases

Thermal Condition : Hot or Cold

Engulfment by finely divided material

Ionizing and non-ionizing radiation

Contact with corrosive substances

Confined Spaces Hazards To evaluate the confined spaces, the following limit values

should be used.

Testing for oxygen Any atmosphere with less than 20.8% (± 0.2%) oxygen

by volume should not be entered. Oxygen measurements should be carried out immediately before entry into the confined space.

Testing for flammable atmosphere A space with an atmosphere with more than 5% of the

“Lower Flammable Limit” (LFL) or “Lower Explosive Limit” (LEL), on a combustible gas indicator should not be entered.


Toxic gases/ vapours must be less than the Permitted Exposure Level (PEL). carbon monoxide (PEL <35 ppm)

or any other hazardous materials as determined by the use of the space.

Always test the air at various levels to be sure that the

entire space is safe.

Good Air

Poor Air

Deadly Air

Good air near the opening does

NOT mean there is good air at the

bottom!

Test the Atmosphere

Oxygen Scale

6%

14%

16%

19.5%

21 %

Difficult breathing Death in minutes

Oxygen Scale

Faulty judgment Rapid Fatigue

Impaired judgment & breathing

Oxygen Enriched

Minimum for safe entry

Toxic atmosphere: Toxins are measured in parts per million (ppm). Under no circumstances should anyone enter a confined space exceeding the limits specified below.

An oxygen deficient atmosphere has less than 19.5% available oxygen (O2). Any atmosphere with less than 19.5% O2 should not be entered without an approved self-contained breathing apparatus (SCBA).

The oxygen level in a confined space can decrease because of work being done, such as welding, cutting or brazing, or even corrosion.

The O2 level is decreased if oxygen is displaced by another gas, such as CO2 or N2. Total displacement of O2 will result in unconsciousness, followed by death.


Oxygen toxicity

Oxygen toxicity is caused by exposure to oxygen at partial pressures greater than those to which the body is normally exposed.

Exposures to partial pressures of oxygen above 1.6 bars (160 kPa) are usually associated with central nervous system oxygen toxicity. Since atmospheric pressure is about 1 bar (100 kPa), central nervous system toxicity can occur where ambient pressure is above normal.

Severe cases can result in cell damage and death.

Vessel Entry Requirement

Entry permit system Permit elements Identification & job description Description of the hazard Precautions already taken while preparation Isolations Gas test results Communications Special equipment or precautions Identify entrants and stand by rescue Hot-work permit involved Any other relevant information Issue, authorization and acceptance Competing the permit procedure

Respiratory Protection

Air-Purifying Respirator (APR) Dust Mask

Half Face

Full Face

Powered Air-Purifying Respirators (PAPR)

Supplied Air Respirator (SAR)

Air-line

Hood style

Facepiece style

Self Contained Breathing Apparatus (SCBA)

When effective engineering controls are not feasible to control breathing contaminated air, appropriate respirators shall be used.

Dust Mask Image courtesy: Google Images

Tight -Fitting Coverings

Quarter Mask Half Mask

Full Facepiece Mouthpiece/Nose Clamp


Loose-Fitting Coverings

Hood Helmet

Loose-Fitting Facepiece Full Body Suit


An atmosphere-supplying respirator for which the breathing air source is designed to be carried by the user.

Self-Contained Breathing Apparatus (SCBA)


Positive & Negative Pressure SCBA

An action conducted by the respirator user to determine if the respirator is properly seated to the face.

Negative Pressure Check

SCBA will be either "positive pressure" or "negative pressure" operation. In negative pressure SCBA air is delivered to the wearer when he breathes in, or in other words, reduces the pressure in the mask to less than outside pressure, hence the name "negative pressure". Any leaks in the device or the interface between the mask and the face of the wearer would reduce the protection offered.


Positive & Negative Pressure SCBA

Positive Pressure Check

Positive pressure SCBA addresses this limitation. By careful design, the device is set to maintain a small pressure inside the facepiece. Although the pressure drops when the wearer breathes in, the device always maintains a higher pressure inside the mask than outside of the mask. Thus, even if the mask leaks slightly, there is a flow of clean air out of the device, automatically preventing inward leakage under most circumstances.



Most preventive and control strategies can be placed in one of the following four categories:

Personal protective equipment (PPE)

PPE imposes a barrier between the worker and the hazard but dose nothing to eliminated or reduce the hazard, e.g. safely goggles, face shields, gloves, boots, full-body clothing, respirators.


Engineering controls

Strategies for replacing a toxic material with one that is less hazardous or redesigning a process to make it less stressful. Isolating a hazardous process to reduce the number of people exposed & introducing moisture to reduce dust.

Ventilation

Exhaust ventilation involves trapping and removing contaminated air. Typically used in processes such as abrasive blasting, grinding, polishing, buffing, and spray painting/finishing.


Administrative controls

Involves limiting the exposure of the employees to hazardous conditions using strategies such as, rotating schedules, required breaks, work shifts.

Summary

Definition of toxic substances

Entry Points (Inhalation/ Adsorption/ Ingestion/ Injection

Effects (acute / chronic)

Relationship of Doses and Responses

Dose Threshold/ Lethal Dose/Concentration


Airborne Contaminants (Dusts/ Fumes /Smoke / Aerosols/ Gases/ Vapours)

Summary


Oxygen scale

Respiratory protection


Engineering controls/ ventilation/ PPE/ administrative.

References & Further Reading

David.L. Goetsch, “The Safety and Health Handbook” Prentice Hall, 2000.

D.A. Crowl and J.F. Louvar, Chemical Process Safety: Fundamentals with Applications, 2001 (2nd Edition).

R.G. Smith and J.B. Olishifski, “Industrial Hygiene” Chicago National Safety Council, 1988.

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