BP Process Safety Series, Confined Space Entry-2005
BP Process Safety Series, Confined Space Entry-2005
BP Process Safety Series, Confined Space Entry-2005
Published by
Institution of Chemical Engineers (IChemE)
Davis Building
165189 Railway Terrace
Rugby, CV21 3HQ, UK
IChemE is a Registered Charity in England and Wales
Offices in Rugby (UK), London (UK) and Melbourne (Australia)
2005 BP International Limited
ISBN-10: 0 85295 479 4
ISBN-13: 978 0 85295 479 9
First edition 2005
Typeset by Techset Composition Limited, Salisbury, UK
Printed by Henry Ling, Dorchester, UK
ii
Foreword
Confined space entry is often described as one of the most hazardous activities
to be performed in an industrial environment. Numerous incidents have occurred in the past. This booklet is intended for those operators, engineers and
technicians working on process plant to raise awareness of the issues
surrounding this activity in order to adopt safe designs and practices and avoid
the occurrence of such incidents.
I strongly recommend you take the time to read this book carefully. The
usefulness of this booklet is not limited to operating people; there are many
useful applications for the maintenance, design and construction of facilities.
Please feel free to share your experience with others since this is one of the
most effective means of communicating lessons learned and avoiding safety
incidents in the future.
iii
Contents
1
Confined space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1
1.2
1.3
1.4
1.5
1.6
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
What is a confined space? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Confined space locations in processing plants . . . . . . . . . . . . . . . . . 2
Hazards of confined spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Other dangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Control of access to confined spaces . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1
2.2
2.3
2.4
2.5
2.6
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
Gas testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Order of gas testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas testing for oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas testing for flammable vapours . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas testing for toxic vapours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calibration and maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Taking gas measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Respiratory protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Protective clothing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Common mistakes and pitfalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Emergency rescue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.1
4.2
4.3
4.4
4.5
15
17
19
22
48
50
51
51
52
55
57
59
59
65
69
69
70
71
71
71
74
Test yourself! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Acronyms and abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Acronyms and
abbreviations
BA
Breathing apparatus
BCF
Bromochlorodifluoromethane
CO
Carbon Monoxide
CO2
Carbon Dioxide
CPR
Cardiopulmonary resuscitation
GFCI
H2
Hydrogen
H2S
Hydrogen Sulphide
JSA/JHA
LEL
LOTO
MSDS
MTBE
N2
Nitrogen
O2
Oxygen
OEL
OSHA
PPE
RPE
SCBA
STEL
TEL
Tetraethyl lead
THA
TML
Tetramethyl lead
UEL
88
1
Confined space
1.1 Introduction
It is said that for every person killed in a confined space, nearly two would-be
rescuers are also killed. Confined space accidents are responsible for many
multiple fatality and injury cases and many of the victims have died trying to
rescue fallen colleagues.
A study conducted by a national agency for occupational health and safety
established that an astounding 234 deaths and 193 injuries resulted from 276
confined space related accidents that were reported over three years. These
figures alone demonstrate the deadly potential of confined spaces. Assuming
that not every accident resulted in an injury or death, which is likely to be the
case, a number of these accidents would have had multiple deaths or injuries.
Number of accidents, fatalities and injuries over a 3-year period
(as reported by a national occupational safety and health agency)
276
234
300
193
250
200
150
100
50
0
Accidents
Deaths
Injuries
Large enough
partially
to
enter
at
least
and/or
Storage tanks
Vessels
Furnaces
Towers
Drums
Piping systems
Boilers
Extruder houses
Laboratories
API separators
Ducting
Tunnels
Pits
Wells
Containers
Underground sewers
Catalyst preparation
buildings
Analyser houses
These conditions can be highly lethal and have frequently resulted in serious
injuries and deaths upon entry when proper safety measures have not been
used.
Many of these hazards are made worse than usual when associated with a
confined space.
Some areas may not seem like confined spaces but may be designated so
because of the presence of specific hazards such as:
displacement;
depletion;
chemical reactions.
An individual entering a confined space with a very low oxygen level usually
shows no warning symptoms but collapses immediately. Death will result
unless the individual is quickly rescued.
Refer to the BP Process Safety Booklet Hazards of Nitrogen and Catalyst
Handling for more information on asphyxiation by nitrogen.
Effects of lack of oxygen
O2
21%
1519 %
12 14 %
10 12 %
8 10%
6 8%
4 6%
Take care when planning or performing a job to ensure that all types
of hazards have been identified and that confined spaces are not
inadvertently introduced.
Oxygen enrichment
There is an increased risk of fire and explosion from high oxygen levels. At
these levels, they can be expected to be more violent and intense.
Higher than normal oxygen levels can result from oxygen leakage during
oxy/acetylene welding operations.
Flammable atmosphere
A gas mixture is flammable when the concentration of flammable material in air
is within the Lower and Upper Explosive Limits (LEL and UEL). A flammable
mixture presents a fire and explosion risk that can kill or injure.
High levels of oxygen, which can occur from leaking oxygen canisters, widens
the range of Lower and Upper Flammability Limits thereby increasing the
possibility of fire.
The ignition of a flammable atmosphere within a confined
space is particularly dangerous because there are
limited means of escape, and the depletion of oxygen
coupled with smoke and heat generation can quickly
render a person unconscious and unable to escape.
Perform gas tests after vacating any confined space for a period
of time, such as for a break, to ensure that safe working conditions
are still present.
Never store
compressed gas
cylinders/tanks in a
confined space,
regardless of their
contents.
Toxic atmosphere
Toxic materials can result in many different adverse health
effects, ranging from mere itchiness to death. The severity
of a human bodys reaction depends on the material,
concentration, duration of exposure, method of entry into
the body and individual susceptibility. The most common
method of entry into the body within a confined space is
through inhalation.
Some toxic substances typically found in process plants are given below. Can
you add to the list?
Hydrogen sulphide (H 2S)
Hydrogen fluoride (HF)
Hydrogen bromide (HBr)
Hydrogen cyanide (HCN)
Ammonia
Chlorine
Benzene
Toluene
Hexane
Welding fumes
Organic lead
Refractory dust
Cadmium vapour
Catalyst
Vanadium pentoxide
The maximum amount of a toxic material that a person can safely tolerate can
be represented in different ways.
The Short Term Exposure Limit (STEL) on the other hand expresses the
maximum value that a person can withstand for 15 minutes without harmful
effects.
The choice of which value to utilize depends on the purpose of the activity
being undertaken.
Exposure to toxic substances can lead to both short-term and long-term
adverse health effects. Both conditions are undesirable and steps should be
taken to avoid exposure to dangerous amounts of toxic substances. Check
your Material Safety Data Sheets (MSDSs) for the safe working concentration
levels of hazardous chemicals handled at your facility. (Refer to BP Process
Safety Booklet Hazardous Substances Refineries for more information.)
Dangerous levels of substances are easily formed within confined spaces due
to poor natural ventilation. Some toxic atmospheres result in death almost
immediately, while others can impede the ability of a person to escape the
area, eventually leading to death.
Although hydrocarbons are mostly regarded as fire and explosion risks, many
have narcotic effects on humans. Initial signs are typical of intoxication. Failure
to respond to verbal commands occurs roughly at the Lower Explosive Limit
(LEL), corresponding to about 50% of the general anaesthetic dose required for
surgical operations. These narcotic effects can occur very quicklywithin only
four breaths!
10
11
12
See BP Process Safety Booklet Safe Ups and Downs for Process Units for
more on pyrophoric scale.
13
HYDROTREATER
REACTOR EMPTY OF
CATALYST
UNDER
NITROGEN
PURGE
SEAL CONNECTION
NOT FULLY
TIGHTENED
Ebullating Bed
Pump
NITROGEN LEAK
TECHNICIAN
CONNECTING UP
MOTOR SEMIASPHYXIATED
OXYGEN DEFICIENT
ENVIRONMENT
Reactor Skirt
14
2
Confined Space
Entry Permit
2.1 Confined Space Entry Permit
What is a Confined Space Entry Permit?
A Confined Space Entry Permit is a document that carefully controls the entry
of personnel into confined spaces. It needs to be filled and signed by relevant
authorities before entry can take place. The permit provides a written
authorization for entry into a confined space and functions as a control system
for this potentially hazardous activity.
A confined space permit is not a replacement for a safe system of work. It is an
extension of it.
location of work;
description of work;
names of entrants and standby attendants;
permit validity period;
process and electrical isolation information;
gas test results with gas testers name and signature;
information on the remaining hazards;
precautions to be undertaken;
rescue procedures;
approval by the Issuing Authority;
acceptance by the Performing Authority;
confirmation on completion of work;
entry cancellation and permit withdrawal.
15
ENTRY PERMIT
NO.
Permission is given to
Location of Work
Item Description
Description of Work
5.
Validity of Permit
Issued on: Date............................Time.........................(hrs)
Expires on: Date............................Time.........................(hrs)
a)
b)
6.
COLD WORK PERMIT NO. ............................ EXCAVATION PERMIT NO. ..................... HOT WORK PERMIT NO. ......................
Others ................................................................................................................................................................................................
Electrical Isolation
6B.
Description and Item No. ................................................................... have been isolated on COLD WORK PERMIT NO. ..........................................
6C.
7.
(Calibrated on ..............)
OTHERS
TIME
DATE
Hazards Remaining:
8.
Gloves/Boots
Dust Respirator
9.
10.
Print Name.......................................................................................
Signed............................................................................................
Time................................(hrs) Date..................................................
SRC
Contractor
Signed ............................................................
Signed ...............................................................
*All works must stop and all personnel must evacuate the confined spaces immediately if the refinery fire alarm sounds or if requested to
do so by an SRC representative. When the "all-clear" fire alarm is sounded, the performing Authority will report to the respective Issuing
Authority to confirm that the areas are safe and work can be resumed.
11.
SRC
Contractor
Signed ..........................................................
12.
Signed ...............................................................................................
Signed .............................................................................................
RENEWAL: The work area has been surveyed and conditions have not changed.
From
Date
Time
VALIDITY EXTENDED
Issuing Authority
To
Date
Time
Name
Signature
Location
Oxygen
Recertification
Flammable Others Certified Gas Testers
Name/ Signature
Gas
16
Before
entry
During
entry
ensures that the job starts and continues to be carried out in a safe manner;
prevents entry by unauthorized persons.
After
entry
2.2 Definitions
Confined space
17
ACCIDENT
Issuing Authority
Note:
Performing Authority
18
Competent Person
Entry Supervisor*
Authorized Entrant*
Attendant/Standby Person*
Permit Requiring:
19
Note: Door
has mesh for
ventilation
Vessel skirt manhole is closed by a locked door
20
The supervisor
entered the
underground
tank through this
manhole even
though the area
had been cordoned off.
21
If yes carry out a risk assessment, set up a safe system of work and do the job
without entering the confined space.
If no a risk assessment must be carried out by a Competent Person. Key
factors to be considered in the assessment would include:
22
suitable equipment;
PPE and RPE;
gas supplies, by pipelines, hoses and cylinders;
entry and exit;
fire prevention;
lighting;
static electricity;
emergency procedures;
working time limits;
anything peculiar to the industry or works concerned, for example,
radioactivity.
Smoking in a confined space must be prohibited and this restriction may extend
beyond the confined space itself.
23
b)
c)
d)
Ventilate
e)
f)
g)
24
steam;
water;
inert gas;
air.
Refer to BP Process Safety Booklet Hazards of Steam and BP Process Safety Booklet
Hazards of Trapped Pressures and Vacuum for more details.
Water is often used to clean long lengths of lines where steam cannot be used
effectively because of rapid condensation in the system. It can also be used to
displace vapour space, but care must be taken to ensure that structural strength
is maintained and to avoid potential for corrosion problems. Water left inside
equipment may freeze in cold weather and should be drained after flushing.
25
Water in
Water in
Some residual oil may remain after lines are flushed with only water. Light oil
flushing may sometimes be employed to remove deposits before water wash.
Inert gas can be used to displace flammable gases from a system. It may not
gas free because of oils left behind in sludge and dead ends, but it can reduce
oxygen levels to below the flammable range. Air can be used to purge tanks
only if no flammable mixtures can be created. Never use air if pyrophoric
materials are likely to be present.
If nitrogen is used to purge, this may influence gas testing and result in
inaccurate readings. Refer to Section 3.2 for details.
continued
26
Hot work
above seal
Sparks
T
a
n
k
w
w
a
ll
ll
B A NG
BANG
Pontoon
Roof
Roof
Water
27
location;
line number, size, and rating;
dates of installation/removal;
signatures of persons confirming each change in position of the mechanical
isolation device.
An isolation/blinds list can help facilitate the activity and ensure that no step is
omitted.
Locking out and tagging out
ACCIDENT
A worker cleaning the inside of a vessel was killed when
the (wrong) mixer was inadvertently started. Electrical
isolations must be locked out and tagged out, and each
vessel should have an isolation list.
In preparation for work within a confined space, all pipes or lines connected to
the space must be positively isolated from live systems by blinding/blanking or
disconnection ensuring that all open ends of adjoining pipes are blinded/
blanked or plugged.
The only acceptable means of isolation are blanking/blinding or disconnecting.
Use of simple valve isolation (even including double block and bleed, which is
closing and locking/tagging a drain or vent valve between two closed valves)
is not an acceptable means of positive isolation for confined space entry.
28
Blanking
PRESSURE
SIDE
BLANK
FLANGE
Securing
Secure mechanical moving parts within confined spaces such as mixers and
fans using latches, chains, chocks, blocks, or other devices.
29
30
31
Nitrogen
under
pressure
Top converter
Inner baffle
Lower converter
32
d) Ventilate
Ventilation is required to obtain an atmosphere
that is as safe as possible for entry. There are
two forms of ventilationnatural and forced
(which includes general and local exhaust).
The adequacy of natural ventilation depends
upon:
ensure that toxic or hazardous substances are not vented directly to the
atmosphere or close to areas that are accessible to workersprovide for
appropriate disposal of exhaust gases;
check that no ignition sources are present for an exhaust of flammable gases.
Ineffective ventilationcontaminated
exhaust circulates back into the space
33
For large tanks, use equipment with sufficient power to ventilate the
entire space or use a series of fans as shown above
The placements of supply and exhaust points are important to obtain effective
ventilation. For contaminants lighter than air, place the exhaust through an
opening at the top of the confined space, while for contaminants heavier than
air, purge is performed at the base of the confined space. Refer to Material
Safety Data Sheets (MSDSs) for the relative densities of gases handled at
your site.
34
ACCIDENT H2S vented from a vacuum truck into work area gases
twelve!!!
An amine knock-out drum had been drained to an atmospheric sump through
an open sewer. A vacuum truck was called to the sump area to begin
pumping out operations. (All amine sumps at the site are either partially or
entirely drained of their contents using vacuum trucks.)
Since it was generally accepted by the employees that pumping out operations
of this manner produces H2S-like odours (the amine contains hydrogen
sulphide gas), no further thought was given to the presence of the strong smell.
Unwittingly, a number of contractors walked through the vapour coming from
the vacuum trucks vent and, as a result, twelve contractors were diagnosed
to have been exposed to an amine cloud containing H2S. Two of them were
disoriented while eleven suffered from vomiting. Fortunately, all returned to
work following a medical evaluation and there were no lost time injuries.
When venting toxic, inert, or flammable gases, make sure the venting
area is far away from the work area, roads, etc. and cordon it off.
See Chapter 3 for details on gas testing requirements and methods, and refer to the
IP Guidance on the declassification of tanks previously in leaded gasoline service.
f) Check that all hazardous energies are controlled or eliminated
Entry into a confined space is prohibited until both Permit Issuing and
Performing Authorities perform the appropriate visual evaluation and
atmospheric monitoring of the space. This includes at least one site survey to
identify and inspect the worksite or equipment.
It is vital that the work area be given a thorough examination to identify any
remaining hazards, inside and outside the confined space, and to see that any
threats they pose are controlled or eliminated.
35
36
a)
b)
c)
d)
e)
37
Lighting
Confined spaces often do not receive sufficient natural
lighting. A safe light source has to be provided to enter
and work in a dark confined space. Regular lighting may
be unsafe to use, especially if the space contains
flammable materials. A spark from an unsafe light
source can cause a fire or explosion, leading to injury or
deaths.
Lightsticks
Explosion-proof droplight
Electrical tools
In certain confined spaces where the hazard of electrical shocks is present
(such as inside metal tanks), suitable precautions need to be taken. These
include using extra low voltage equipment (typically less than 25V) and, where
necessary, residual current devices.
38
Communications equipment
Communications equipment is often given low
priority when preparing for a confined space entry
but is usually the first thing we turn to instinctively
when something goes wrong. Communication
procedures should be appropriate for the workplace
and level of risk. It can be achieved by voice, radio,
hand signals, or other appropriate means depending
on the conditions. A continuous voice communications system is the preferred means.
A battery charging and changing regime should be in place to ensure that the
user is aware of the status of the equipment and that the procedure is
performed as recommended by manufacturers.
Ingress and egress equipment
For confined spaces that require vertical access,
ladders are usually installed to facilitate entry. Most
installed ladders are made of metal and may have been
shrouded in moist, chemical-laden atmospheres prior
to purging and ventilating. These conditions promote
corrosion and the ladder may fail during entry or exit.
Installed ladders must be inspected on a
periodic basis to ensure that they are safe
for use. It is important to also check the
devices holding the ladder, such as
attachment bolts and screws.
39
When ladders or stairways are not available for safe entry and exit, winches
and hoisting devices are commonly used to raise and lower entrants. Only
hand-operated lifting devices should be employed. Do not use motorized
devices as they continue to pull an entrant out, even when the entrant gets
caught up in an obstruction, resulting in severe injuries or a fatality.
Ensure that winching and hoisting devices used for entry into a
confined space never leaves the entry/exit point when the confined
space is occupied to provide a ready means of retrieval.
40
Rescue services
Check that means of rescue and rescue services are present and on standby.
It is essential that adequate help is available at all times to allow a quick and
effective rescue to be carried out. (Refer to Chapter 4 for details on rescues)
b) Inform personnel of the confined space entry requirements
All entrants and standby attendants must be thoroughly briefed on the full
requirements for the confined space entry. The hazards present must be clearly
stated and understood. Entrants must also be careful not to introduce
additional hazards into the area, for example using sparking tools when
flammable vapours are present.
41
Entrants must know the hazards and mitigation measures, and must be able to
recognize changing conditions that invalidate the Confined Space Entry Permit.
The permit must be available at all times at the work location.
Wearing suitable and properly maintained Personal Protective Equipment (PPE) is
absolutely vital when hazardous conditions warrant it. See Section 3.8 for details.
Do not enter a confined space unless every precaution specified in
the entry permit is fulfilled.
Smoking is strictly prohibited in a confined space!
c) Entry to perform activity
Double check against the work order and entry
permit that the correct equipment is to be entered.
fire extinguisher;
additional radios for communication;
spare oxygen bottles (for SCBAs and cascade system);
first aid kit.
42
the entrants can alert the standby attendant whenever any warning signs or
symptom of exposure to a dangerous situation is recognized;
the entrants can call for help in an emergency and the standby attendant, in
turn, summons rescue services;
43
44
45
46
preparing the area for safe entry by proper planning and identification of
risk;
arranging gas testing;
interpreting gas test results and making the decision to proceed;
authorizing and issuing the Confined Space Entry Permit;
ensuring that a properly trained standby attendant is present during entry;
monitoring the conditions within the confined space for changes;
ensuring that a rescue plan is in place and emergency personnel are
informed.
ensuring that personnel are aware of the hazards that are present;
checking that only safe tools are used in the confined space (such as nonsparking);
47
48
49
Lessons learned
50
3
Gas testing and PPE
requirements
3.1 Gas testing
Atmospheric testing must be conducted by an authorized Gas Tester to:
51
A test for oxygen is performed first because most combustible gas meters
rely on the presence of oxygen to function and will not provide reliable
readings in an oxygen deficient atmosphere. Combustible gases are tested
for next because the threat of fire or explosion is both more immediate
and more life threatening, in most cases, than exposure to toxic gases and
vapours. If tests for toxic gases and vapours are necessary, they are
performed last.
O2
Basic electrolyte
(e.g. a solution of
potassium hydroxide)
Gold
cathode
Lead
anode
Thermistor
V
Voltmeter
Oxygen Analyzer
Working principle
The most common oxygen sensor works on an electrochemical principle. The
oxygen diffuses through a plastic membrane into the interior of the
electrochemical cell, where it produces a low electric current between the gold
cathode and the lead anode. This signal is amplified and transmitted to the
indicating instrument and to the alarm unit.
52
No gas present
Gas present
No output signal
Output signal
proportional to gas
Electrochemical Cell
The electrolyte solution requires a specific gas (such as oxygen) to
generate an output signal. Other gases have no effect. When the gas
enters the cell, it produces a signal that is proportional to the amount of gas
present.
X%
100 Y%
Where
X % vol of oxygen (as measured by your oxygen analyzer)
Y % of contaminant gas
For instance, if x 19.0%, then y 8.7%.
Note: A reduction of 1.8% of oxygen in air means the presence of 8.7% of a
contaminant gas or vapour.
Normal
Air
Air with
contaminant Y
79.2% nitrogen
72.3% nitrogen
20.8%
oxygen
19.0%
oxygen
100%
100%
With contaminants in air, the normal percentages of oxygen and nitrogen are reduced to
smaller values. Knowing the new and smaller value of O2% from the oxygen analyzer,
the percentage of the contaminant in air can be calculated.
53
Oxygen-enriched atmosphere
If the measured oxygen level is above 20.8%, it is most likely that a nearby
oxygen cylinder or source is leaking. This condition is equally dangerous as an
oxygen-enriched atmosphere (23.5%) will cause flammable materials such
as clothing, hair and oils to ignite more easily and burn violently. Remember to:
Refer to BP Process Safety Booklet Hazards of Air and Oxygen for more
details.
The lead anode is used up over time and the sensor must be replaced every
one to two years.
54
Working principle
The Wheatstone bridge is balanced under zero explosive conditions at ambient
temperature. Air is flushed several times through the instrument which is then
adjusted to zero using a single rheostat which adjusts the circuit balance and
detector current simultaneously. This is done every time before a test is
performed.
The sample is drawn into the cell by pumping the aspirator bulb (flame
arrestors must be in place to prevent flame propagation). Heat is developed as
the flammable mixture in the sample burns on a heated catalytic platinum
filament forming part of the bridge. The filament temperature is raised; hence
the resistance is raised in proportion to the heat of combustion in the sample,
which is directly dependent upon the concentration of combustibles. A bridge
imbalance occurs, the meter is deflected on a scale calibrated directly as %
Lower Explosive Limit (LEL).
55
Precautions/limitations
Remember this instrument measures the % LEL. It does not measure the
true concentrations of the flammables. It does not measure the concentration beyond LEL. For vapour above the LEL, the instrument will flick over
and then return to zero, giving a false sense of safety. However, your
oxygen results from earlier measurements should give you an indication of
how much flammable material there is.
0% vol
5% vol
15% vol
LEL
100% vol
UEL
flammable range
20% LEL
0% LEL
100% LEL
The measurement range for most flammable gas detectors is only a fraction of the LFL.
For instance, the flammable range of methane is between 5% (LEL) and 15% (UEL)
by volume, but only the first 5% is monitored by most detectors.
56
Temperature variation. Ethyl alcohol easily evaporates at atmospheric conditions, resulting in a cooling effect that causes concentration equivalent of
LEL to give only 66% LEL on a conventional explosimeter.
High flash point materials such as lubricating oil, diesel oil or fuel oil is often
heated during maintenance/repair work, giving rise to a flammable
atmosphere. This will be undetected if the gas test is only done before the
work starts, not continuously. If gas testing is carried out during the work, the
explosimeter may not be able to detect heated vapours of high flash point
materials because condensation will occur in the sampling tube. It is
uncommon to obtain an explosive reading of a vapour with a flashpoint
above ambient temperature. Cutting up oil drums with 1/10th pint oil left in
them will form an explosive mixture as the oil is vapourized. Testing devices
are not always entirely reliable. Visual inspection is essential.
Leakage of air into the instrument through loose connections will cause a
dilution effect and give lower readings.
Draeger tubes
57
Working principle
The equipment consists essentially of a hand-held bellow pump and a
detector tube appropriate to the toxic compound to be measured. It is a
convenient sampling system and makes use of specific chemical colorimetric
reactions.
Method:
Advantages
Its main advantages are its convenience, speed of response and speed in
terms of obtaining a quantitative answer.
Limitations
Store in cold. Each tube has specific instructions including storage life,
which is usually two years, although stock turnover of not more than six
months is preferable.
58
Various fixed and portable gas detectors with visual, audible and/or vibrator alarms
There is a large range of fixed and portable toxic gas detectors available for
use in detecting the full range of typical gases including H2S, CO, CO2,
benzene, etc. In order to be effective, these devices need to be maintained
and calibrated regularly to provide adequate assurance. The sensors are often
sensitive and can be easily damaged.
The duration of testing should be at least the minimum response time of the
test instrument specified by the manufacturer.
59
continued
60
61
ACCIDENT Have you gas tested at all levels and in all areas?
A vertical reactor vessel (7.6 m/25 ft high) had been safely shut down, the
catalyst removed, water washed twice, ventilated, inspected, gas tested and
approved for entry. Then, the vessel was left idle for five days with no
mechanical ventilation. Gas testing was carried out again in preparation for
entry but was done only in the area around 2.4 m (8 ft) from the top manhole.
The reactor was then approved for entry by operations. The contractor went
down the ladder with an employee at the top manhole who lowered an
explosimeter/gas sentinel simultaneously with the entrant. No mechanical
ventilation was installed for this entry. Halfway down the vessel, the gas
sentinel alarmed due to a high LEL. The entrant immediately ascended the
ladder and exited the vessel. He felt a headache and was sent to the hospital.
continued
62
This incident could have resulted in a fatality or serious injury to the entrant
from a flash fire or being exposed to toxic levels of hydrocarbons. Although no
visible liquid hydrocarbon was detected in the vessel, hydrocarbon vapour
was probably released from residues trapped behind the metallic reactor
shroud or absorbed into the refractory liner. Gas testing at the manhole was
definitely not representative of the entire internal working space. This incident
clearly highlights why it is important to perform gas testing for top, middle,
and bottom of confined spaces. Remember to gas test at all levels and in all
areas.
Comment
An Authorized Gas Tester/Test Person is a person nominated by local
management to undertake gas tests of confined spaces. Such a person will
have received training in the use of the particular gas measuring instruments.
However the responsibility for WHAT and WHERE to test for contaminants
remains with the Confined Space Entry Permit Issuing Authority, who may also
be the nominated Authorized Gas Tester.
Other precautions
Even after an empty tank has been purged, toxic or flammable gases can
desorb from porous walls or be liberated from sludge, cleaning solvents or
produced by chemical reaction between sludge and solvents or other
materials.
63
The minimum safe level of oxygen in the air for working is 19.5% (which
is not far below the normal level in the air of 21%). Refer to BP Process
Safety Booklet Hazards of Nitrogen and Catalyst Handling for more
details on the dangers of inert gas atmospheres and working in confined spaces.
64
Flammable
Toxic
20.8%
<1% LEL
<10% OEL
19.5-23.5%
up to 20% LEL*
up to STEL
<19.5% or >23.5%
>20% LEL
>STEL
Entry without
breathing apparatus
Specific risk assessment
Unsafetoo high for
normal breathing apparatus
Oxygen
Flammable
< 1% LEL
20.8%
up to 20% LEL*
< 1% LEL
< 1% LEL
>23.5%
or
<19.5%
up to 20% LEL*
Toxic
<10% OEL
up to STEL
> STEL
<10% OEL
up to STEL
> STEL
<10% OEL
up to STEL
> STEL
<10% OEL
up to STEL
> STEL
<10% OEL
up to STEL
> STEL
<10% OEL
up to STEL
> STEL
<10% OEL
up to STEL
> STEL
<10% OEL
up to STEL
> STEL
<10% OEL
up to STEL
> STEL
Entry without
Breathing
Apparatus
Specific
Unsafe
Risk
Too High
Assessment for normal BA
**
65
Types of
atmosphere
Safe
atmosphere
Hazardous
atmosphere
Lifethreatening
atmosphere
66
Entry requirement
Strictly No Entry!
See Note 1*.
Strictly
No Entry!
67
Picture of the separator after the incident, with inadequate physical barrier
and lack of signage.
warning devices for low breathing air pressure should be installed and
tested prior to the commencement of work.
68
69
4
Emergency rescue
4.1 Rescue and emergency services
The site should have a procedure describing the means of rescue and
allocation of resources (internal and/or external) to affect a confined space
rescue, and the means of raising the alarm.
Rescue should always be considered when planning for confined space entry
work. In all cases of entry into confined spaces the methods of rescue of
persons from inside the equipment must be agreed upon in advance with the
appropriate emergency services function, irrespective of whether breathing
apparatus is worn.
The hazards that may be faced during entry including information on the mode
of exposure, signs or symptoms, and consequences of exposure shall be
communicated to the entrants and standby person.
All entrants should exit from a permit required confined space as quickly as
possible whenever:
the entrant detects a prohibited condition, for example, toxic level exceeds
STEL.
resuscitation techniques;
raising, and responding to the alarm;
safeguarding rescuers;
fire control;
plant control;
first aid;
on-site, and off-site, emergency services;
70
training.
Each member of the rescue team is provided with, and is trained to properly
use, the personal protective equipment and rescue equipment necessary
for making rescues from confined spaces.
Each member of the rescue team shall be trained to perform the assigned
rescue duties. Each member of the rescue team shall also receive the
training required of authorized entrants.
Each member of the rescue team shall practice making confined space
rescues at least once every 12 months, by means of simulated rescue
operations in which they remove dummies, mannequins, or actual persons
from the actual confined spaces, or from representative confined spaces.
Representative permit spaces shall, with respect to opening size,
configuration and accessibility, simulate the types of confined spaces from
which rescue is to be performed.
Each member of the rescue team shall be trained in basic first-aid and in
cardiopulmonary resuscitation (CPR). At least one member of the rescue
team holding current certification in first aid and in CPR shall be available.
4.4 Lifeline
When entry is made wearing breathing apparatus, all entrants must also
wear a full body harness and lifeline that extends outside the confined
space.
71
Each authorized entrant shall use a chest or full body harness, with a
retrieval line attached at the centre of the entrants back near shoulder level,
or above the entrants head. Wrist harness may be preferable to a full body
harness in the case of a closed vessel provided with one or more manholes.
The other end of the retrieval line shall be attached to a mechanical device
(such as a tripod and winch assembly) or fixed point outside the permit
space in such a manner that rescue can begin as soon as the rescuer
becomes aware that rescue is necessary.
72
A means must be provided for both safe normal entry or exit, and emergency extrication.
Ladders may be used for ordinary entry and
exit. Tripods with hoist, lifeline, and full
body harness are often used for emergency
rescue and recovery.
73
74
Should conditions develop which require extrication, and the entrants cannot
get out of the confined space on their own, the standby person must call for
emergency assistance at once!
The standby person should attempt to remove the entrant from the confined
space using tripods, hoist, and lifelines. The Standby Person must NEVER
enter confined spaces. Lethal hazards may be present within the confined
space. Only properly equipped and trained emergency rescue personnel may
enter confined spaces to make rescues.
75
76
77
5
Some points to remember
1.
2.
3.
4.
5.
78
6.
7.
8.
9.
79
21. If the confined space fails the gas test, take time to
examine the situation and carry out proper planning
before repeating preparation steps.
80
26. Double check against the work order and entry permit that
the correct equipment is to be entered.
81
82
83
Acknowledgements
The co-operation of the following in providing data and illustrations for this
edition is gratefully acknowledged:
iv
Bibliography
ANSI Z117.1
API 2217
API 2015
OSHA 29 CFR
89
Test yourself!
Confined spaces
1.
One of the first questions that should be answered before planning entry
into a confined space is can this job/task be accomplished without
entering the space?
True
2.
False
False
7.
False
6.
False
A confined space has limited or restricted means for entry and exit.
True
5.
4.
False
3.
False
A worker can access the roof of an empty floating roof tank (20 ft/6 m of
height) without a Confined Space Entry Permit because there is no
product in the tank.
True
False
9.
False
The most deadly hazards associated with confined spaces are hazardous
atmospheric conditions and engulfment.
True
84
False
10. If an employer decides to contract out all confined space work, then they
will not need to develop an effective Confined Space Entry Program.
True
False
11. A written Confined Space Entry Permit Program requires that the employer
develop a system to prepare, issue and cancel entry permits.
True
False
the permit must include the purpose, date and duration of entry;
the permit must list all residual hazards and necessary precautions;
a rescue plan must be attached to the permit.
True
False
13. The type of ventilation methods to be used for confined space entry is
determined by the configuration and contents of the confined space, and
the tasks to be performed inside it.
True
False
False
15. Local exhaust ventilation is not required for welding work in a confined
space.
True
False
False
17. When contracting out all confined space work, the employer does not need
to ensure that the contractor has a proper rescue plan.
True
False
False
19. The following must be included in employee training for confined spaces:
85
Gas testing
False
20. The proper gas testing sequence for confined spaces is the following:
Toxics; Flammables; Oxygen.
True
False
False
False
False
24. Toxic gases in confined spaces can result from products stored in the
space and the manufacturing process; work being performed inside the
space or in adjacent areas; desorption from porous walls and
decomposing organic matter.
True
False
25. It is the duty of the standby attendant to continually test the level of toxic
chemicals in the confined space.
True
Standby attendant
False
26. A standby attendant is a person with no other duties assigned other than to
remain immediately outside the entrance to the confined space and who
may render assistance as needed to personnel inside the space. The
attendant never enters the confined space and never leaves the space
unattended while personnel are within the space.
True
False
27. The standby attendant watches over a confined space while other
employees are in it and can only leave to use the restroom.
True
False
28. A standby attendant is a person who runs to the nearest food store to buy
refreshments for the crew inside the confined space.
True
86
False
False
30. Standby attendants can enter the space to rescue a worker but only when
wearing a SCBA and connected to a lifeline.
True
Rescue team
False
31. During most confined space incidents, outside personnel tend to risk
personal safety to rescue others affected inside the confined space.
True
False
32. The employer shall provide trained confined space rescue personnel for
each confined space entry affected.
True
False
33. The rescue personnel must be on site, must be aware that confined space
entry is being performed, and must be immediately available to perform
rescue.
True
False
34. Each member of the rescue team will practice making rescues at least
once every year.
True
False
35. Each member of the rescue team need not be trained in basic first-aid and
cardiac-pulmonary resuscitation (CPR).
True
False
ANSWERS
1T/2T/3F/4T/5F
6T/7F/8F/9T/10F
11T/12T/13T/14F/15F
16T/17F/18T/19T/20F
21T/22T/23F/24T/25F
26T/27F/28F/29F/30F
31T/32T/33T/34T/35F
87