Hot Work Gas Testing - OPITO Unit AGT2
1 Introduction to the course
1.1 Purpose of the Training Course
1.2 Summary of each classroom-training module
1.3 Summary of the practical session undertaken both in the classroom and in the workplace
2 Properties of flammable and toxic gases
Flammable gases: A study of the physical properties of:
(A) Natural Gas
(B) Propane
(C) Butane
(D) Crude Oil Vapours
(E) Solvents
(F) Hydrogen
Assessment for each regarding:
- Explosive limits
- Gas cloud formation
- Movement of gas clouds
- Densities of pure gases
- Gas dispersion
- Densities of gas clouds
- Effects of ventilation
- Autoignition temperature
- Flash point
Toxic gases: A brief study of the toxic gases met in the clients industry, their characteristics from an awareness point of view, noting the differences between asphyxiating and toxic gas atmospheres and an overview of the COSHH Regulations and EH40, Workplace Exposure Limits, 8 Hour and 15 Minute exposure limits and units of measurement.
3 Gas Sensors
Flammable Gas Sensors: Catalytic gas sensors - how they work and what causes them to become unreliable and fail, catalytic "poisons" and "inhibitors", the effects of silicones, Halon, water and other contaminants,"ambiguity" effects at high gas concentrations - thermal conductivity sensors used for inert gas purging operations - infra-red gas detection - the importance of regular calibration.
Toxic Gas Sensors: (A) Electrochemical cells for the detection of oxygen, carbon monoxide, carbon dioxide and hydrogen sulphide - how they work and what causes them to become unreliable and fail. (B) Chemical detector tubes and other sensing methods.
4 The clients range of gas detectors
The Portable Gas Detector, description of your detectors, explanation of readings obtained, pre-issue testing, sources of error and malfunction and how to both recognise and reduce instrument failures - using for demonstration purposes, one example of each gas detector and sampling system
5 Certification for hazardous areas
5.1 The certification label and its location
5.2 Thermite sparking and static hazards
5.3 Gas Detectors, repair and maintenance rules
6 Written multiple-choice question assessment test
Results of the MCQ assessment test and discussion
7 Practical session in classroom and on-site
7.1 Understanding the methodology of hot-work gas testing - the Thinking Process
7.2 Explaining the Hot Work Assessment Criteria and competency assessment
7.3 Preparing the hot-work gas detector for use
7.4 Practical gas testing on-site for both gas and condensate leaks - evaluation of trainee competence, in the workplace, against defined assessment criteria by means of observation, questioning, simulation and/or inspection of output.
Read about the 35ft rule for hot work [see right column]
8 De-brief from practical session
End.
The "35ft rule"
The "35 ft. rule" for hot work, is a standard that has been in place in North America for the past 15+ years. The distance of 35 ft. is really an evolution built from analysis of the minimum separation for grade level hot work based on loss history in the USA and Canada. This distance has stood the test of time and as such has been adopted as the minimum. FM Global has conducted some recent testing on hot work blankets, which demonstrated the validity of the 35 ft. rule.
The key to the "35 ft. rule" is hot work conducted on grade level. For elevated hot work, there is no set safe distance as too many factors can be involved that affect the hazard created and each situation needs to be evaluated on the physical conditions present. Loss history has also shown 35 ft. to be inadequate for elevated hot work activities (inside and outside).
For occupancies where flammable liquids or gases are involved with the production process, the 35 ft. rule for hot work can still be applied effectively with added safeguards. However, use of a non-hot work method for whatever work is involved should always be the first option of choice. If hot work must be conducted, the least hazardous form of hot work should be used like heliarc welding vs. electric arc stick welding.
The best advice when flammable liquid/gas occupancies are involved is for all equipment/piping within the 35 ft. zone to be completely drained, cleaned and purged. Lock-out/Tag-out procedures should be implemented on all flammable liquid/gas systems in the area. If the process systems cannot be drained/purged, this equipment should be shut down and completely shielded from the hot work operation with proper welding screens/blankets. Mechanical low-level ventilation should be maintained within buildings housing flammable liquid/gas process equipment/systems when hot work is being conducted.
Continuous LFL monitoring with portable units should be posted at multiple points within the 35 ft. safe zone around the hot work with procedures in place to immediately stop all hot work if LFL monitoring equipment registers flammable vapours/gases of any percentage. This would include both sides of any equipment isolation welding screens/blankets. Fire watch personnel should be posted in the area of hot work and the LFL monitoring equipment to ensure the area remains in a fire safe condition throughout the hot work activity and sixty (60) minutes following completion of the hot work.
Outside environments create an added challenge to conducting safe hot work when flammable liquid/gas processing or distribution equipment/systems are involved. Even with extensive monitoring for LEL concentrations, wind conditions can introduce flammable vapors/gases into the hot work hazard area and create a dangerous condition before LFL monitoring and the personnel involved with this hot work activity can react. The hazard and risks involved will be heavily dependent on the specific flammable materials involved and the quantity of flammable environment introduced.
For any hot work within high hazard occupancies like flammable liquids or gases, this work should be well planned and coordinated to hopefully eliminate but at least minimize the fire risks involved.
This information was kindly provided by: Mark E. Blank Chief Engineering Technical Specialist FM Global Midwest Field Engineering - Park Ridge Office (847) 430-7606