Some of the gasses we work with can be very dangerous, so we need to make sure the atmosphere is safe to work in Before any work starts
during the time the work is taking place
INTRODUCTION TO GAS TESTING Q. Who can carry out gas testing? A. Only those people who have attended Authorized Gas Tester training can certify a gas test.
INTRODUCTION TO GAS TESTING The following abbreviations are used: AGT - Authorized Gas Tester. CH 4 - Methane (a flammable hydrocarbon gas). H 2 S - Hydrogen Sulphide (a toxic gas). LEL - Lower Explosive Limit. UEL - Upper Explosive Limit. ppm - Parts per million.
All AGT’s must have completed TIJD Permit to Work training before becoming an Authorized Gas Tester.
There are THREE reasons why we do gas tests:
To make sure there are no toxic (poisonous) gasses present in the air, and that the atmosphere is safe to breath.
To make sure there is sufficient Oxygen in the air to support life.
To make sure there are no explosive gasses, and so minimise the possibility of an explosion happening.
In phases 6,7& 8, we test for the following: H 2 S and SO 2 under certain circumstances, it is possible that these toxic gasses can be found in the atmosphere. Methane this explosive gas could be present if there was a leak in the (CH 4 ) processing equipment or many flow lines. Oxygen Before we enter any ‘ Confined Space ’, we must make (O 2 ) there is sufficient life supporting oxygen to support human life.
Where should we expect to find explosive gas? Hazardous Area Classification The classification in zones or “zoning” is the partition of the installation into volumes in which a flammable atmosphere may be present (refer to the definition of a hazardous area). • Zone 0 That part of a hazardous area in which a flammable atmosphere is continuously present, or present for long periods. • Zone 1 That part of a hazardous area in which a flammable atmosphere is likely to occur in normal operation. • Zone 2 That part of a hazardous area in which a flammable atmosphere is not likely to occur in normal operation, and, if it occurs, will exist only for a short period.
What hazards exist in these locations?
Voids/cofferdams Casing vents Drain valves Valve spindles Empty flow lines Flanges Low points Sludge Open pits/ditches High points Open drains Most important places to be tested
Explosive Limits All combustible gases and vapours have an ‘explosive limit’, between which the gas or vapour, mixed with air, is capable of sustaining the spread of flame. These can be referred to as the ‘explosive’ or ‘flammable’ limits .
15 Too Rich IMPORTANT! 100 5 0 Upper Explosive Limit (UEL) Lower Explosive Limit (LEL) Not enough gas (to create an explosion) % Methane (CH 4 ) IN Air Too much gas (not enough oxygen to support combustion) Explosive Range (for Methane)
The lower explosive limit (LEL) refers to the lowest concentration of a gas in the atmosphere which results in a combustible mixture. For example, the LEL of Methane in Air is 5% by volume. This means that if there is less than 5% by volume of Methane in air the mixture is too lean to support combustion . When Methane Gas Test equipment indicates 100% LEL, there is 5% by volume of Methane in the test atmosphere.
The Upper Explosive Limit (UEL) refers to the highest concentration of a gas in the atmosphere which results in a combustible mixture. For example, the UEL of Methane in air is 15% by volume, which means that if there is more than 15% of Methane in the air by volume the mixture is too rich to support combustion.
THINK! UEL If an atmosphere exceeds the UEL, then as the gas slowly disperses, it will have to pass through its ‘explosive range’ before it gets to its LEL. This is a very the dangerous time!
Some other examples of LELs and UELs Note that meters must be calibrated for each individual gas.
For most practical Gas Testing purposes it is the LEL which is significant . The AGT is responsible for recording the percentage of LEL for the specific flammable gas being tested on the permit.
TOXIC GASES The two main toxic gasses we are concerned with in Kharg are: SULPHUR DIOXIDE SO2 HYDROGEN SULPHIDE (SULFIDE) H2S Important Note: H2S is ALSO EXPLOSIVE
Main Characteristics of H2S:
Heavier than air.
Readily dispersed by wind or air currents.
Flammable - burns with a blue flame.
Odour of rotten eggs (below concentration of 100ppm).
Highly corrosive to certain materials (e.g. steel).
H2S Long-term exposure limit. (LTEL) (over on 8 hour reference period) of 10ppm. Short-term exposure limit. (STEL) (over a 10 minute reference period) of 15ppm. The way in which H 2 S affects you depends on the length of time the individual is exposed, and on the concentration
It is possible for the Gas produced on Phases 6, 7& 8Kharg to contain up to 0.85% H2S 0.85% = 85,00ppm
Sulphur Dioxide SO2 SO2 is not combustible but is hazardous to health. Low level alarm 2ppm High level alarm 5ppm Precautions If SO2 is detected - vacate the area.
Definition of Confined Space: Any place which can trap gas.
POTENTIAL HAZARDS IN CONFINED SPACES
TOXIC OR FLAMMABLE GASES
LOW OXYGEN CONTENT
ROTATING OR MOVING EQUIPMENT NOT ISOLATED
FLUID OR GAS INLETS OR OUTLETS NOT ISOLATED
RESIDUE FROM PREVIOUS CONTENTS
SLIP TRIP OR FALL HAZARDS
LACK OF ADEQUATE LIGHTING
DANGEROUS CIRCUMSTANCES Concentrations of gases or vapors can arise from sources both inside and outside confined spaces. Some examples are:
Gas or vapor remaining from a process which has previously been carried out in the confined space. DANGEROUS CIRCUMSTANCES
Oxygen content may be low or absent due to a variety of reasons
Purging with Inert Gas such as nitrogen
Displacement by other gases from adjoining plant area
Depletion due to oxidation ( rusting ) of metals
Depletion due to fire or welding / cutting process
Low Oxygen remains as the single biggest hazard in Confined Spaces
Gas or vapor from adjoining plant due to ineffective isolation. Fumes emitted when sludge deposits are disturbed during inspection / cleaning... DANGEROUS CIRCUMSTANCES
Fumes produced by an operation inside a confined space, e.g. welding, flame cutting, lead lining, rubber lining, brush and spray painting, molding GRP (fiberglass), use of adhesives, solvents , etc.
The production or combustion of various fuels.
TESTING CONFINED SPACES The tests should check for the presence of gas or toxic fumes and the adequacy of the supply and content of Oxygen .
TESTING CONFINED SPACES The tests must start from outside the confined space, and/or the AGT must wear a SCBA.
TESTING CONFINED SPACES Never enter in a confined space without a stand-by man.
TESTING CONFINED SPACES Gas can be trapped at a high level. The tests must be done at different places and at different levels.
MSA ORION MULTI-HEAD GAS MONITOR AfSTC
TESTING CONFINED SPACES NOTE: An acceptable result must be obtained before work in any area proceeds. L.E.L - 0% C0 - 0 PPM H2S - 0 PPM 02 - 20.8 %
Gas tester must be re-calibrated every 6 months, or after having shown a great amount of gas.
Miniwarn gas detector with telescopic probe
The battery charge will be reduced by running the pump.
Make sure no liquids are allowed to enter the probe because it will damage the sensor heads
Important When performing an atmospheric test for a confined space put the probe into the confined space, NOT your head .
Meters must be calibrated IN ACCORDANCE WITH MANUFACTURERS RECOMMENDATIONS (normally every 6 months) Meters must be calibrated by Drager or AN AUTHORISED AGENT . Do not use meters without an in-date calibration sticker.
This training course is for gas testing only . All persons who enter a confined space for work must undergo specific “ Confined Space Entry” training.
Confined space entry Any space or void w ith difficult access/egress, and/or an atmosphere which has the potential to cause you harm What is a confined space?
Important Ordinary ‘explosimeters’ (gas detectors) DO NOT WORK if the oxygen level is below 15% When a vessel has been purged with nitrogen to remove hydrocarbons, an ordinary gas detector will not work. A special meter, or chemical detector tubes, must be used to check for hydrocarbons.