Ventilation by a blower, eductor or fan may be necessary to remove harmful gases and vapors from a confined space. There are several methods for ventilating a confined space. The method and equipment chosen are dependent upon the size of the confined space openings, the gases to be exhausted (e.g., are they flammable?), and the source of makeup air.
Under certain conditions where flammable gases or vapors have displaced the oxygen level, but are too rich to burn, forced air ventilation may dilute them until they are within the explosive range. Also, if inert gases (e.g. carbon dioxide, nitrogen) are used in the confined space, the space should be well ventilated and re-tested before a worker may enter.
A common method of ventilation requires a large hose, one end attached to a fan and the other lowered into a manhole or opening. For example, a manhole would have the ventilating hose run to the bottom (see diagram) to exhaust all harmful gases and vapors. An air intake should be placed in an area that will draw in fresh air only.
Ventilation should be continuous where possible, because in many confined spaces the hazardous atmosphere will form again when the flow of air is stopped.
De-ballasting a tank does not guarantee a safe atmosphere. Testing is still required.
A standby person should be assigned to remain on the outside of the confined space and be in constant contact (visual or speech) with the workers inside.
The standby person should not have any other duties but to serve as standby and know who should be notified in case of emergency. Standby personnel should not enter a confined space until help arrives, and then only with proper protective equipment, life lines, and respirators.
It has been closely monitored and observed that: Over 50% of the workers who die in confined spaces are attempting to rescue other workers.
Rescuers must be trained in and follow established emergency procedures and use appropriate equipment and techniques (lifelines, respiratory protection, standby persons, etc.). Steps for safe rescue should be included in all confined space entry procedures. Rescue should be well planned and drills should be frequently conducted on emergency procedures. Unplanned rescue, such as when someone instinctively rushes in to help a downed co-worker, can easily result in a double fatality, or even multiple fatalities if there are more than one would-be rescuers.
Isolation of a confined space is a process where the space is removed from service by:
- locking out electrical sources, preferably at disconnect switches remote from the equipment.
- blanking and bleeding, securing valves Cargo, ballast, IGS, pneumatic and hydraulic lines
- disconnecting mechanical linkages on shaft-driven equipment where possible, and
- securing mechanical moving parts within confined spaces with latches, chains, chocks, blocks, or other devices.
Basic surveyor PPE must be taken into account
- Body protection (hard wearing overalls with suitable pockets for notebook etc).
- Foot protection (steel toecaps (200 joules), steel midsoles, good grip, oilresistant).
- Head protection (hard hat with chinstrap).
- Hand protection (hard wearing gloves).
- Eye protection (protective glasses, goggles).
- Ear protection (ear defenders or ear plugs – worn subject to communication system).
- Lighting (hand held torch with lanyard and appropriate beam width).
Do not enter a confined space until you have considered every question as well as any other item of concern, and have determined the space to be safe.
The final decision is yours. Is entry necessary? Will someone accompany you into the space?
- Are the instruments used in atmospheric testing properly calibrated?
- Was the person performing the tests a certified Marine Chemist, Competent Analyst, or equal, or a (competent) person designated by the facility or vessel management to so?
- Was the atmosphere in the confined space tested?
- Was Oxygen at least 19.5% – not more than 21%?
- Were toxic, flammable, or oxygen-displacing gases/vaporspresent?
- – Hydrogen sulfide
- – Carbon monoxide
- – Methane
- -Carbon dioxide
Points to pounder are :
Checklist for enclosed space entry :
|Section 1 – PRE-ENTRY PREPARATIONS||Yes||No|
|1*||Has a formal risk assessment been prepared and discussed by the personnel entering the space ?|
|2*||Pre-entry atmosphere test readings ( using portable monitors ) Tested By :-
Oxygen………..……………………% vol (21%), Time : –
Hydrocarbon………………………%LFL (less than 1%),
Toxic Gases(CO/H2S/Benzene)……..………………….ppm(less than 50 % TLV-TWA of the specific gas)
|3*||Have arrangements been made to repeat atmosphere testing of the space during occupancy and during breaks?|
|4*||Are access and illumination adequate?|
|5*||Have arrangements been made to continue ventilation of the space during occupancy and during breaks?|
|6*||Is rescue and resuscitation equipment available for immediate use by the entrance to the space?|
|7*||Has an attendant been designated to be in constant attendance at the entrance to the space ?|
|8*||Has the Officer of the Watch (Bridge, ECR, CCR) been advised of the planned entry?|
|9*||Has a system of communication between all parties been tested and emergency signals agreed?|
|10*||Is a record maintained for the personnel entering/exiting the space?|
|11*||Are Lock Out tags/notices in place where applicable?|
|12*||Are Plant isolation referred to where applicable?|
|13*||Are portable lights and other equipment available and an approved /certified type?|
|14*||Are personnel entering the space equipped with personal monitors?|
|ADDITIONAL CHECKS TO BE CONDUCTED FOR SPACES/TANKS OTHER THAN PUMPROOM|
|1.||Has the space been cleaned, where necessary?|
|2||Has the space been tested at different levels and locations, using portable monitors?|
|3||Has the space been positively segregated by blanking off or isolating all connecting pipelines or valves and electrical power/equipment ?|
Section 2 – PRE-ENTRY CHECKS
To be recorded by the person authorized as LEADER of team entering the space
|1.||I have checked Section 1 of this permit and confirm it has been completed fully?|
|2.||I am aware that the space must be vacated immediately in the event of ventilation failure or if atmosphere tests change from agreed safe criteria?|
|3.||I have agreed upon the procedure for communication?|
|4.||I have agreed upon a reporting interval of ……………..minutes|
|5.||I have agreed and understood the emergency and evacuation procedures|
|6.||I understand the work to be carried out. We have discussed and agreed the safety measures and I’m satisfied it is safe to commence work||Name/Rank /Signature of team leader entering space|
|SECTION 3 : AUTHORISATION|
|I am satisfied that all appropriate safety measures are in place and that the work can be conducted safely.||Chief Officer|
|Work Authorised By:||Master / Chief Engineer|
|SECTION 4 : PERMIT CLOSURE/CANCELLATION|
|Equipment /system has been de-isolated and returned to the “in-service condition”|
|All notices and tags removed|
|The work area and equipment is in a safe condition|
|Work Completed||Permit is time Expired||Work suspended|
|Permit Closed By:
(Chief Officer/Chief Engineer/Master)
|Signature :||Date :
- Gas samples should be taken using portable gas instruments, from several depths and through as many openings as possible in order to get a good cross section representation of the compartment’s atmosphere. Ventilation should be stopped for about 10 minutes before pre entry atmosphere tests are taken.
- Only those entries marked * need to be completed for pump room entry.
- Chief Officer is authorised to sign/close the permit, ONLY for routine pump room entry/inspection.
- Copy of the permit is to be displayed on site.
- TLV-TWA for various gases – CO – 25 PPM, H2S- 5 PPM, BENZENE – 1 PPM