Class notes topic 5

TOPIC 5 : WASTE TREATMENT AND DISPOSAL TECHNOLOGY
Outline of topic 5:
AIR CONTAINMENT
GENERAL VENTILATION AND LOCAL EXHAUST SYSTEMS
CONFINE SPACE SAFETY MEASURE

Introduction
WHAT IS YOUR UNDERSTANDING?
• Who are you ?
• What is your role?
• We have any ISSUES for these?
• Are you important for this ISSUES…….?

What is ventilation?
 Ventilation is the process of supplying and removing air by
natural or mechanical means to or from any space.
 It is used for heating, cooling and controlling airborne
contaminants which affect employees and the general
environment.
 Industrial ventilation emphasizes the control of toxic and/or
flammable contaminants

What is Industrial Ventilation?
 Industrial ventilation generally involves the use of supply and
exhaust ventilation to control emissions, exposures, and
chemical hazards in the workplace.
 Traditionally, nonindustrial ventilation systems commonly
known as heating, ventilating, and air-conditioning (HVAC)
systems were built to control temperature, humidity, and
odors.

Ventilation may be deficient in:
• confined spaces;
• facilities failing to provide adequate maintenance of
ventilation equipment;
• facilities operated to maximize energy conservation;
• windowless areas; and
• areas with high occupant densities.
Any ventilation deficiency must be verified by measurement.

What are confined spaces?
A confined space means any place in which, by virtue of its enclosed
nature, there arises a reasonably:
 foreseeable specified risk of fire or explosion
 loss of consciousness of any person due to an increase in body
temperature
 loss of consciousness or asphyxiation of any person due to gas, fume,
vapor or lack of oxygen
 drowning of any person due to an increase in the level of liquid
 asphyxiation of any person who is trapped by a flowing solid
Confined spaces include any chamber, tank, vat, pit, well, sewer,
tunnel, pipe, flue, boiler, pressure receiver, hatch, caisson, shaft or silo.

HAZARDS IDENTIFICATION
1. Deficiency of oxygen in air
Air generally comprises 21% oxygen. However, in the following
conditions, the oxygen in the air may decrease, resulting in a menace
with human life:
 Chemical reactions caused by oxygen consumption
- oxygen is consumed due to oxidation during such processes of
welding, rusting, naked flame operations, fermentation and moulding.
 Substitution
- oxygen is squeezed out by such inert gases as nitrogen, argon and
carbon dioxide.
 Adsorption on surface
- oxygen is adsorbed by porous surfaces, such as activated carbon.

Changes of the oxygen content in air that is breathed in, can cause the
adverse physical reactions to the human body.

2. Flammable spaces
 Flammable gas in a confined space can lead to explosion or fire.
 A space becomes flammable when oxygen in the air mixes with flammable
gases, vapors or dust.
 These gases and vapors may be formed by residues mixed with flammable
substances, the use of flammable substances, or chemical reactions (e.g.
the formation of methane).
 A space may also become flammable when combustible dust abounds or
flows in the air when disturbed.
 Dust may come from agricultural products e.g. flour, chemicals, plastic
particles, medicine or metal powder.
 Flammable spaces will explode when contact with igniting sources such as
welding sparks or sparks from portable electrical appliances.

The explosive range of flammable gases or vapors
(percentage in air)

CHEMICAL SUBSTANCES
 The principal means of encountering chemical substances include:
- respiration
- skin absorption
- eating.
 The effects brought by chemical substances upon the human body may
be chronic or acute, depending on:
- the period of contact (how long get contact with chemical
substances)
- the intensity of the hazards during contact (how dangerous the
chemical substances)
- the impact of such hazards on health (example: corrosive,
toxic or harmful)

PHYSICAL HAZARDS
1. Mechanical hazards
-some dangerous components such as belts, rotation shafts and gears in equipment
may cause harm when used.
2. Electrical hazards
- risks of death caused by electric shock or getting burn may arise when touching
electric cables, electric wires and transformers in confined space.
3. Noise hazards
-noise produced when working in confined spaces is generally higher than normal
(leading to impairment in worker’s hearing and may even lead to deafness).
4. Radiation hazards
- sparks produced when using radioactive equipment in confined space may cause
harm (laser or welding sparks).
5. Environmental hazards
- environmental conditions are more likely to pose danger in confined spaces
(extremely high or low temperature, dampness, wet spaces)
6. Transportation hazards
- sewer are situated on road, workers will have the risk of being knocked down by
vehicles passing by.
7. Engulfment by liquid or flowing flow
- flowing solids such as silt may pose the risk of engulfment.

Mechanical &
Electrical hazards
Noise hazard Environmental
hazard
Transportation
hazard
Engulfment by liquid
Engulfment by flowing
solids

OTHER HAZARDS
1. Hazards from manual operations
- The working environment of confined spaces is generally narrow and
workers inside need considerable effort when performing manual
operations.
2. Biological hazards
- Workers may be infected with different varieties of bacteria and viruses
and even threatened by biological hazards produced by insects and
snakes.

General Ventilation and Local Exhaust
Systems

 Thousands of workers contract occupational asthma and other lung
diseases each year.
 Many people die or are permanently disabled by these conditions and are
unable to work.
 People develop those diseases because they breathe in too much dust,
fume or other airborne contaminants at work, often because control
measures do not work well enough.
 Most industries are affected, including woodworking, welding, paint-
spraying, stonemasonry, engineering and foundry work.
INTRODUCTION

Employers are often unaware that their workers are being
overexposed to these substances or the existing controls may
be inadequate. The problems include:
 Source of exposure are missed
 Employers (and supplier) are over-optimistic about the
effectiveness of the controls
 Existing controls are deteriorated
 The controls are not used correctly

 General (dilution) ventilation systems supply clean air that
mixes with the air in the workplace, diluting the concentration
of the contaminant.
 General ventilation is not suitable to control exposure to toxic
substances because these systems actually spread the
contaminant throughout the workplace before exhausting it.
 General ventilation systems are used primarily to control
temperature and humidity, to remove odors, and sometimes
to remove traces of toxic substances and microorganisms
emitted from carpeting, paneling, furniture, and people.
GENERAL VENTILATION

‘General exhaust ventilation, also called dilution ventilation, is
different from local exhaust ventilation because instead of
capturing emissions at their source and removing them from
the air, general exhaust ventilation allows the contaminant
to be emitted into the workplace air and then dilutes the
concentration of the contaminant to an acceptable level
(e.g., to the PEL or below). Dilution systems are often used to
control evaporated liquids. ’

General exhaust ventilation (dilution ventilation) is
appropriate when:
 Emission sources contain materials of relatively low hazard. (The degree
of hazard is related to toxicity, dose rate, and individual susceptibility);
 Emission sources are primarily vapors or gases, or small, respirable-size
aerosols (those not likely to settle);
 Emissions occur uniformly;
 Emissions are widely dispersed;
 Moderate climatic conditions prevail;
 Heat is to be removed from the space by flushing it with outside air;
 Concentrations of vapors are to be reduced in an enclosure; and
 Portable or mobile emission sources are to be controlled.

LOCAL EXHAUST SYSTEM
 Local exhaust ventilation is an engineering control system to reduce
exposures to airborne contaminants such as dust, mist, fume, vapor
or gas in a workplace.
 Local exhaust ventilation systems remove the contaminant before it
spreads through the workplace.
 The systems are designed to take advantage of the motion of the
contaminant in order to capture it without drawing in large
amounts of air as well.
 They are most useful for controlling toxic materials when their
airborne concentrations could exceed legislated standards.

‘A typical local exhaust ventilation system is composed
of five parts: fans, hoods, ducts, air cleaners, and
stacks. Local exhaust ventilation is designed to
capture an emitted contaminant at or near its
source, before the contaminant has a chance to
disperse into the workplace air. ’

COMPONENTS OF A LOCAL
EXHAUST SYSTEM
A local exhaust system consists of four (4) elements:
1. Hoods
- a structure designed to enclose or partially enclose a contaminant-
producing operation and to guide air flow in an efficient manner to
capture a contaminant.
-typical captured velocities required are:
i) 100 feet per minute (fpm) for vapors and gases
ii) 200 fpm or more for dusts
2. Ductwork
- ductwork in an exhaust system is to provide a channel for flow of the
contaminated air exhausted from the hood to the point of discharge.

- typical velocities required are:
i) 1000 fpm for vapors and gases
ii) 4000 fpm for heavy dusts
- the heavier the particle, the greater the velocity needed
3. Air cleaning device (cleaner)
-to remove contaminants from the air stream before it is passed to the
fan and expelled to the atmosphere or recycled to the work area.
- two types of air cleaning devices:
i) air filters
ii) dust collecters
4. Air moving device (fan)
-the device that draws the air through the entire system
- It must be capable of generating enough of pressure drop to draw the
required volume of air through the hood, ducts, and collecting devices at
the correct velocity, and of overcoming the resistance to air flow from
hoods, ducts, and collecting devices.

It is vital to identify all components that may be part of the Local
exhaust ventilation system, for example:
 Parts of equipment such as the machine casing or guards if
they have extraction to control emissions
 Flues from hot processes, e.g: furnaces or ovens
 Systems to replace extracted air (make-up-air), particularly
where large ventilated booths extract large volumes of air
from the workroom

Local exhaust ventilating is appropriate when:
 Emission sources contain materials of relatively high hazard;
 Emitted materials are primarily larger-diameter particulates
(likely to settle);
 Emissions vary over time;
 Emission sources consist of point sources;
 Employees work in the immediate vicinity of the emission
source;
 The plant is located in a severe climate; and

PRINCIPLE OF LOCAL EXHAUST
Basic principles for applying local exhaust ventilation to a specific
problem:
i. Enclose the source as completely as practicable
ii. Capture the contaminant with adequate velocities
iii. Keep the contaminant out of worker’s breathing zone
iv. Supply adequate make-up air
v. Discharge the exhausted air away from air inlet systems

What employers need to do before
applying LEV?
LEV may not be practicable controls as there may be many
sources or extensive contaminants clouds that are too large
for LEV alone to control. The other control options include:
 Eliminate the source
 Substitute the material being used by something safer
 Reduce the size of the source
 Modify the process to reduce the frequency or duration of
emission
 Reduce the number of employees involved with a process
 Apply simple controls, eg: fitting lids to equipment

What employers need to know when
LEV is appropriate?
 The key properties of airborne contaminants.
 How gases, vapors, dusts and mists arise.
 How contaminant clouds move with the surrounding air.
 The processes in the workplace which may be sources of
airborne contaminants.
 The needs of the operators working near those sources.
 How much control will be required.
 How to prepare a specification for the LEV designer.

Employers also need to be aware of:
 the general principles of hood design and application;
 the need for airflow indicators and other instrumentation;
 capture zones, working zones and breathing zones;
 the general principles of ductwork, air movers and air cleaners
and how they interact;
 the principles of how to discharge contaminated air safely and
replace it with clean air;
 the process of installing and commissioning the LEV system;
 the need for a user manual and logbook;
 the requirement for thorough examination and test of LEV.

What employees need to know to
carry out routine checks
 The parts of an LEV system and their function.
 How the LEV system should be used.
 How to recognize a damaged part.
 Simple checks that the LEV system is delivering its design
performance and is effectively controlling emissions and
exposure.

What maintenance and repair
engineers need to know?
 How to recognize and assess hazards.
 How to follow safe systems of work.
 To warn operators that maintenance is under way.
 How the LEV system works.
 What assessment methods to use to check the LEV system’s
performance is maintained.
 What routine maintenance is needed (following instructions
such as those in a ‘user manual’).
 What measures of performance to record and who to report
to if there are problems.

Prevention and Control
‘A well-designed system and a continuing preventive
maintenance program are key elements in the
prevention and control of ventilation system
problems. ’

 Oxygen Deficiency (Asphyxiation)
 Fire/Explosion
 Accumulation of Flammable Vapour
 Overcome by Toxic Fumes
COMMON HAZARDS

Why people enter confined spaces?
Confined spaces are normally entered to perform necessary industrial tasks. The list
below represents some typical reasons for entering confined spaces:
a) cleaning to remove waste or sludge
b) physical inspection of plant or equipment
c) installing pumps, motors or other equipment
d) maintenance work such as painting, sand blasting or applying surface coatings
e) reading of meters, gauges or dials
f) repair work, such as welding or cutting
g) installing, repairing or inspecting cables such as telephone, electrical or fibre
optic
h) tapping, coating or testing of piping systems (e.g. steam, water or sewage)
i) constructing a confined space such as an industrial boiler
j) rescuing people who are injured or overcome by fumes.

VENTILATION IN CONFINED SPACES
 Confined spaces contain atmospheres that are flammable, toxic or whose
oxygen level has been depleted or enriched.
 Natural ventilation is generally insufficient to remove contaminated air
from the inside space and to exchange it for fresh air from the outside.
 The lack of air exchange occurs particularly in confined spaces that have
few openings for access and due to the configuration of the confined
space itself.
 They can be effectively ventilated with apparatuses that move the air and
remove the contaminated air from the confined space introducing:
- clean,
- breathable air, and
- controlling the level of danger

BASIC REQUIREMENTS OF VENTILATION
Although a single rule or group of rules is unlikely to cover all of the
ventilation requirements applicable to confined spaces, the objectives
of ventilation in confined spaces are the following:
 To remove contaminated air (flammable or toxic) from the space and
maintain safe concentration levels in terms of permissible exposure
level (PEL) or lower explosive limit (LEL), using the most convenient
one.
 To provide fresh and breathable air inside the space.
 To create a more comfortable environment inside the space.

VENTILATION BEFORE ENTERING OR
WORKING
Confined spaces must be ventilated before entering or
working to the degree necessary to reduce
flammable and toxic substances to acceptable levels
and to provide adequate oxygen content inside the
space.

VENTILATION TO ENTER AND WORK
Ventilation requirements to enter and work in confined spaces
depend on the nature of the space, its content, and the
operations that will be performed inside the same.
The operations that are performed inside a confined space
may require the application of a single type of ventilation,
such as general ventilation, or may require the application
of two types, such as general ventilation combined with a
local exhaust ventilation system.

1. General Ventilation
-Refer to general ventilation as the action of exhausting or supplying air
for breathing and for climate control inside the space, that is, ventilation
to control the heat.
2. Local Exhaust Ventilation
-To remove the contaminants that are generated in a single point, as in
welding, or in localized clean-ups with solvents, local exhaust systems are
more effective.
3. Dilution Ventilation
- Occasionally, this ventilation mechanism must be used in circumstances
where the operation or the process performed prohibits the use of local
exhaust ventilation.
4. Dilution and Exhaust Ventilation (entry and exit / push/pull)
- Type of ventilation consists of incorporating uncontaminated air inside a
space to dilute contaminants, combining them with an exhaust localized
at the area of greatest generation of contaminants, utilizing flexible
ducts.

VENTILATION OF FLAMMABLE
ATMOSPHERES
The fans, exhausts, motors and other equipments that are use to
ventilate atmospheres that contain vapors, emanations, fogs,
dusts, etc., flammables or explosives, must be equipments
that are essentially safe by design, such as fans with
pressured air jets, eductors, or vapor ejectors, etc.
The equipment must be properly insulated and grounded, as
appropriate, to control the accumulation of electricity and
discharges.

VENTILATION SYSTEM ARRANGEMENTS
Ventilation systems must be arranged to provide the best possible air
distribution to all the space and the air must be of breathable quality so
that it replaces the contaminated air that is removed from the space.
1. Air Circulation
-The location of the exhaust and air intakes for the exchange is extremely
important to achieve a proper distribution of air throughout the confined
space.
2. Replacement Air
-The replacement air that is fed to a space to replace the contaminated air
must be clean and contain normal levels of oxygen that can be breathed.
3. Exhaust Air Outlets
-Exhaust air containing flammable or toxic substances must be ventilated
to the exterior atmosphere to a place where the contaminants can be
diluted and dispersed.
4. Lighter or Heavier than Air Contaminants
-In a confined space, contaminants that are lighter or heavier than air tend to
accumulate in greater concentration in higher or lower areas, respectively.

A RISK MANAGEMENT APPROACH FOR
CONFINED SPACES
The Workplace Health and Safety Act 1995 (the Act) describes a
five step risk management process by which hazards can be
managed. The process entails:
Step 1: Identify hazards
Step 2: Assess risks associated with the hazard
Step 3: Decide on control measures to prevent or minimize the
level of risk
Step 4: Implement the control measures
Step 5: Monitor and review the effectiveness of the control
measures

Step 1: Identify the hazards
 analysing injury and incident records
 talking with workers about their experience or problems which may arise
 conducting a task analysis
 consultation with designers, manufacturers and suppliers of confined
spaces
 obtaining advice from occupational health and safety specialists,
engineers or occupational hygienists
 consultation with unions, employer associations, professional bodies or
government associations
 using scientific or technical information (e.g. atmospheric testing, reports,
safety alerts or journals).

Step 2: Assess the risks
Once the hazards have been identified, the associated risks
for each hazard should be assessed. There are three major
factors to consider when assessing the risk of hazards (the
likelihood of an incident occurring and the consequences)
First – determine the likelihood
Second – determine the consequences
Third – rate each risk

Step 3:Deciding on control measures
When the hazard cannot be eliminated measures must be taken
to control the risk of death, injury or illness.
The hierarchy of control presents control measures in an order of
priority. The higher order controls provide a greater level of
protection against a risk.

Step 4: Implement and
review control measures
 Providing training and instructions on what the control
measures are, how they work, any changes to the controls
(including why the changes need to be made)
 Adequate supervision to ensure that the controls are being
used correctly
 Maintenance procedures – for example, releasing a pressure
valve on a service line
 Communication procedures between staff and supervisors –
for example, monitoring controls or when new
problems/situations arise
 Measuring the effectiveness of controls

CONTROL MEASURES FOR CONFINED
SPACES
1. Elimination – the ideal solution would be to eliminate the
confined space hazard altogether, by eliminating the need to
enter the space.
2. Substitution – involves replacing a hazard or work process
with a less hazardous one.
3. Isolation and engineering – this involves modifying the
workplace, plant or process to physically distance the worker
from the hazard. Isolating the worker from the hazard can
also be effective.
4. Atmospheric testing – shall be carried out consistent with
the hazards identified and the risk assessment.

1. Gas Monitoring
TYPICAL CONTROL MEASURES
Gas monitoring by HSE
personnel
Confined space status
chart

2. Adequate Ventilation and Lighting

CONFINED SPACE-SAFE ENTRY POLICY
 When requested to enter a confined space:
i) Only enter a confined space when a permit to enter has been issued
ii) If you consider it is safe to do so
iii) Only remain in the inside for as long as it is necessary to carry out the
work
 It is full responsibility of the owner of the confined space to ensure
that the confined space is safe to enter:
i) The surveyor has the right to refuse to enter an unsafe or unknown
space
ii) If he is not confident that a space is safe, he should report his concerns
and not to enter until all safety requirements are met.

CONFINED SPACE-SAFE ENTRY PROCEDURE
Prior to entry an enclosed space the following procedure should be applied:
a) A Safety meeting should be held prior to the survey to discuss all aspects
of safety measures
b) Entry Permit should be obtained for the space to be entered
c) Identify the hazards and assess the risks
d) Evaluate ventilation of the space
e) Evaluate need for isolation of the space
f) Ensure that a standby and rescue team is in place
g) Check and evaluate gas measurements taken
h) Evaluate need for precaution against extreme temperature
i) Evaluate the lighting arrangement
j) Evaluate if special clothing and equipment are required

PERMIT-TO-WORK and PERMIT-TO-ENTER
A permit-to-work will:
 set out the work to be done, the location and the precautions to be
taken
 predetermine safe methods of work
 provide a clear record that all foreseeable risks have been considered
 define the precautions to be taken and their sequence
 provide written authority for the confined space to be entered and the
work to start and the time when the work must cease.
Entry into a confined space should only be allowed when a separate
permit-to-enter has been issued.
(this permit should only be issued after tests have taken place to ensure that the
atmosphere is safe to breathe)

TESTING OF THE ATMOSPHERE
 Initial testing should be carried out by a certified “Marine Chemist” or a
“Competent person” or similar accredited person who will issue a
certificate stating whether the space is ‘safe for man’ and/or work, and
if any special conditions are to be observed.
 Ventilation should be stopped about 10 minutes before tests are made
and not restarted until the tests are completed.
 The testing should be carried out in the following sequence
- Oxygen-deficient or -enriched atmospheres
- Flammable atmospheres
- Toxic atmospheres when considered necessary

 To evaluate the measurements taken, the following limit values should
be used.
a) Testing for oxygen
b) Testing for flammable atmosphere
c) Testing for toxic atmosphere
d) Testing instruments

PREPARATION FOR ENTERING
CONFINED SPACES
 Ventilation
-Ventilation should be continuous where possible because in many confined spaces
the hazardous atmosphere will form again when the flow of air is stopped.
 Isolation of space
-The surveyor should evaluate the need for isolation of the confined space from
service before entering the space.
 Standby / Rescue
-A standby person should be assigned to remain on the outside of the confined
space and be in constant contact.
-Rescuers must be trained in and follow established emergency procedures and use
appropriate equipment and techniques (such as lifelines, respiratory protection,
standby persons).

PERSONAL PROTECTION EQUIPMENT (PPE)
 PPE is traditionally regarded as the last line of protection with the emphasis being
placed on avoidance and appropriate managerial control methods.
 Basic surveyor PPE should include:
-Body protection (hard wearing overalls with suitable pockets for notebook)
-Foot protection (steel toecaps, steel midsoles, good grip, oil resistant)
-Head protection (hard hat with chinstraps)
-Hand protection (hard wearing gloves);
-Eye protection (protective glasses, goggles);
-Ear protection (ear defenders or ear plugs – worn subject to communication
system);
-Gas meter - multi-gas meter for measuring of HC, H2S, CO, O2 is recommended
-Lighting (hand held with lanyard and appropriate beam width).

Extent to which a person may be safely exposed to a hazardous substance (typically a
gas or solvent vapor) without endangering his or her health. These limits are generally
discretionary and every country defines its own limits, resulting in a lack of widely
accepted standards.
EXPOSURE LIMITS

Class notes topic 5

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Class notes topic 5