Hazards of Confined Space




Hazards of Confined Space can be classified as

1.      Poor lighting and Ventilation.
2.      Oxygen deficiency
3.      Contamination of Toxic and/ or flammable gases
4.      Unexpected activation of machinery or flow.
5.      No way or no time available for exit.
6.      Engulfment (burying) in loose material.
7.      Non specific work practices. 

Other hazards are suffocation, burning, poisoning, and explosion, Drowning, freezing, Crushing, entrapment, scalding, stroke, heat stress, radiation, physical trauma, injury by moving machinery, slipping or falling etc. 

Many fatal and serious accidents have occurred while working in a confined space. Three reasons flammable air mixture, toxic gases and oxygen deficiency are found responsible {or such accidents. Tanks (vessels) with top cover open but all other sides closed, should be considered as a confined Space, because, in such situation persons working inside have to face direct fire, explosion, or toxic exposure and have no other way to run away except the only way of their entry. Therefore doubtlessly and as per above statutory definition, such situation/condition is a confined space. 

One worker died due to solvent fire, one died due to chloroform vapour and two died due to nitrogen (oxygen deficiency) atmosphere in such confined spaces. 

Confined Space work Permit


Permit for Vessel Entry: 

Work in vessels and tanks below ground in pits, cellars and basements or inside confined spaces such as silos, tanks, vats, vessels, boilers gutter etc., pose danger and always require permit to Work system. 

Definition Confined Space. 

Confined space as any space by reason of its construction as well as in relation to the nature of the work carried therein and where hazards to the persons entering into working inside exist or are likely to develop during working.
                                                       
Confined Space is also described as a place which-
a.       Mostly enclosed and partially open.
b.      Is at atmospheric pressure and tempera hire 
c.       Has limited or restricted openings for entry and exit.
d.       Is not designed or intended for normal place of work (i.e. not for long time worker occupancy)
e.       Has unfavourable natural ventilation due to stagnant air, no free air movement, oxygen deficiency or enrichment or nitrogen atmosphere" 
f.       Has contaminated air with toxic or / and flammable gas, dust etc and 
g.      May cause engulfment (swallowing) in unstable or loose material.

Examples (Types) of confined spaces are
·         Storage tank
·         Process Vessel / Reaction Vessel
·         Pressure Vessel
·         Boiler
·         Tank cars(Truck)
·         Silos
·         Ducts
·         Gutters 
·         Tunnels
·         Tank wagons
·         Sewers
·         Digester
·         Vats 
·         Wells / bores
·          Bilges 
·         Under floor/ Floor opening
·         Shafts
·         Sumps
·         Go-down of grain, sulphur, cement, clay and similar loose material 
·         Pits
·         Roof voids/Gap between roof and Fall Ceilings

Safe entry in any confined space like pit, sump, vessel, vat, tank, chamber, furnace, oven, pipe, flue, gutter or isolated and unknown place needs work permit system. The hazards of work are toxic or flammable gas inside, asphyxiating atmosphere, accidental inflow of chemical or starting of agitator etc. 


Vessel Entry Permit under section36(2) of the Factories Act 1948, no person in any factory shall be required or allowed to enter any confined space (chamber, tank: vat, pit, pipe, flue etc. having dangerous fumes .likely to involve risk) until all practicable measures have been taken to remove any fumes which may be present and to prevent any ingress of fumes and unless a certificate in writing has been given by a competent person based on a test carried out by himself that the space is free from dangerous fumes and lit for persons to enter or such person is wearing suitable breathing apparatus and a safety belt securely attached to a rope (life line) the free end of which is held by a person outside the confined Space. 

Isolation of the vessel from sources of energy or harmful substance by way of cooling, disconnection, blinding, blanking etc, draining, cleaning, washing and purging; to make free from toxic gases, testing the air for oxygen or toxicity content, opening top and bottom connections for good ventilation; lighting and exit, wearing safety belts, helmet and suitable breathing equipment, allowing low voltage (24 volts) light. Standby arrangement etc.are essential requirements.

More danger is foreseeable when any gas or vapour visible or invisible, having odour or not heavier than air (vapour density > 1) is suspected in the confined space. Fatal cases have been reported. No person should enter or allow another person to enter such situation without going through the following steps: 

1.        Report the need of such entry to higher officer whose duty is to prepare and sign a necessary work permit for such work. 
2.        Work permit will be prepared after observing the situation from outside, allowing the vessel to be cooled and giving full thought to all the safety points to be incorporated. 
3.         If it is an underground pit, sump, chamber or tank having no connections except a manhole at the top, the manhole should be opened after wearing a self breathing apparatus, free air movement and venting should be allowed for some time and then the gas test and the oxygen level test should be carried out. Toxic gas should be safely driven out by air purging and a flammable gas by nitrogen purging. The worker doing this job should be experienced and wearing self breathing apparatus. Such work should be carried out during day time with good natural lighting. While replacing any flammable gas or hydrocarbons, sources of ignition must have been removed and non-flameproof electric lighting/fitting de-energised. Only a flameproof torch may be used. To avoid static electricity, airline should be bonded with the metal of the vessel 
4.        After evacuating gases as above, again their level (PPM in case of toxic gas and percentage in air LEL-in case of flammable mixture) should be measured and brought down to a safe level. But this is not sufficient. Oxygen content should also be measured and it should be more than 18%, otherwise specific instruction of SCBA shall he mentioned in the work permit. 
5.        If it is a vessel, tank, reactor, pipe or other space having nozzles and connections, first top and bottom, vent and drain/ flush valves should be opened to discharge lighter and heavier gases. Inlet connections should be isolated, blinded or removed from joint. By nitrogen purging inner gases should be fully pushed out. Then the vessel should be washed and drained by steam and water if it is not incompatible. Then the manhole and other top and bottom connections should be removed making the top-bottom nozzles fully open for better (cross) ventilation and lighting. This ensures that neither heavier nor lighter gases will remain inside and free entry of air will keep the Space breathable. Otherwise positive air supply should be provided. If it is not possible to open any joint except manhole, the procedure stated in pont 3 and 4 should be followed. 
6.         After ensuring ambient condition and isolation or disconnection of inlet lines, opening maximum nozzles possible (at least flush bottom drain and top vent), removing or isolating any common connection (e.g header or common vent or scrubber line) and measuring gas and oxygen content to a safe level, electric connections (e g. driving motors for stirrer, pump, blower, exhaust, vacuum or any ingress or egress of material) shall be removed (by removing fuses and indicated by a warning notice and tagging) and the overall situation shall be verified for safe entry.
7.         Only after assessing the real need of entry and verification as above, the work (vessel entry) permit shall be signed and safety precautions mentioned in it shall also be verbally explained to the permit holder and the worker who has to enter inside. The issue of permit should be done by a responsible and experienced person only 
8.         If it is not possible to achieve safe working level inside due to presence of toxic gas or less oxygen content, the condition of self breathing apparatus and a safety belt having its free end (life line) in the hands of a capable person standing outside to pull him out, and first aid and rescue/reviving apparatus in ready condition, shall be clearly mentioned in the work permit and explained to the workers and supervisor. 
9.         lf work is to be carried out of replacement of any pyrophoric catalyst under nitrogen blanketing or of removal of any deposit, scale, sludge, waste or lining inside, instructions stated in point 8 shall be strictly observed. 
10.      Now-after receiving the permit, it shall be fully understood before execution. All conditions shall be fulfilled including wearing SBA, safety belt and necessary equipment. Environment shall be cool for entry and safe working. Manual bell may be carried to give signal of any emergency situation and indication to pull the life line or supplying anything necessary. 
11.      Air line respirators are not safe because of the possibility of detachment of air supplying pipe. . Canister gas masks are also not-advisable. A self breathing apparatus with low pressure alarm seems to be the safe remedy.
12.      After the work is over, the permit shall be signed and returned to the person who issued it. Experience or suggestion if any shall be mentioned to make the future work safer. 

If the work cannot be completed in one shift or within time limit mentioned in the permit, the permit should be submitted for extension before continuing the work.

No statutory format is available. A company can device a format best fitting to their nature of jobs. Items to be included in such format are Place of work, work to be done, whether withdrawal from service, isolation, cleaning and purging, testing, conditions, expiry time and authorisation to work, acceptance of certificate, completion of work, extension is required, permission of extension, cancellation of the permit and provision for signature, date and time.

Isolation of pipelines and electric power should be positive and effective. Mere closing of valve or switch is not sufficient. 

If a worker inside becomes unconscious or is in trouble, entry for rescue shall be allowed with SCBA, safety belt and other persons standing outside to pull 'the life line(with head up) lf this is not done multiple fatalities are possible.



Ergonomic Consideration for Plant Design and Layout


    Important ergonomic Factors to be considered in Plant layout and Design include:

1.       Free space (80 to 100 cm) around each Machine for easy and safe Movement.
2.       No overcrowding, Breathing space of 14.2 M3 Per worker( Max height 4.2 M)
3.       Ventilation Operation – 15% of the floor area minimum. Window bottom height 1 meter or less from the working floor for natural ventilation.
4.       A Traversing part of materials carried by machinery should not approach with in 50 Cm of any fixed structure which is not part of the machine.
5.       Suitable platforms, Safe means of Access lifting appliances suspension points should be provided to facilitate cleaning and Maintenance work.
6.       Height and position of the seats, Valves, gauges, Indicators, Switches, push buttons, Breaks notices etc., Should be suitable to the operation. Safe manual lifting methods should be utilised.
Types of Ergonomic Design are as under:
S.no
Types
Includes
1
Working space Design
Seat, Bench or console( Control or comfort) design, Positions of Controls, displays and materials, operator’s body, data and their working models including computer graphics
2
Environmental design
Light, Ventilation, Humidity, Noise, Vibration etc. Comfortable to the operator.
3
Work time or Situation Design
Working Hours, Intervals, Shift schedule and inter-personal aspects of work
4
Interface Design
Exchange of information between man and machine or environment e.g. display gives and control receives information. Proper design of display (Pointers, letters, numbers, figures, etc.) and controls (Knobs, brakes, switches, size, shape, position, forces, etc.) most convenient to the men
5
System Design
Allocation of function/job between man and machine and procedure. New technique to understand limitation of each other and to fill the gap by the best design.
   
   All these are overlap and interrelated. The main object of ergonomic design to get long term gain with no adverse effects on health and safety and to minimise human errors, efforts, stress and strain and ultimately risks and accidents.
   Workplace design calls for following ergonomic factors.
1.       Standing position, offers more mobility, more arm strength application, less front to rear room, no seat and greater latitude in work station design
2.       Sitting position offers forceful pedal operations, less fatigue, precise vision.
3.       Work object or job position should be close to the front edge of the work surface to avoid more bending or leaning.
4.       Sufficient room for hands and feet movement with footrest and backrest to work while sitting.
5.       Visual display should be in front of the body and below eye level so that the lines of sight are declined 10 to 40 degree below the horizontal level.
6.        Avoid holding time of work piece or hand tool to minimise muscle tension.
7.       Use lever mechanism to apply less force. Take advantage of mechanical design, appliance, equipment, instrument etc. To reduce manual work
8.       Foot controls for seated operators, soft floor(e.g. rubber mats) for standing operator, adjustable chair to maintain proper sitting height, permitting posture change to avoid fatigue, allowing sitting/ standing alteration and enough space for working are all to be considered  in ergonomic design.
9.       Computer operators have posture and vision Complaints, e.g. musculoskeletal pain & discomfort, eye strain and fatigue. Studying the position, furniture, equipment, lights etc. Should be redesigned. Upright trunk and neck position, forward set surface, properly shaped backrest and properly placed controls and displays are necessary.