allowable threshold , unless preventive measures are available and agreed to by owner such as the use Breathing Apparatus , though this is not preferred as it hinders job execution .
For all CSE activities , we MUST ensure sufficient ventilation for the personnel working in the Confined Space . In order to determine the amount of ventilation needed , one can refer to local legislation as stated below together with the sample Engineering Calculation Steps .
According to the Factories and Machinery ( Safety , Health and Welfare ) Regulation 1970 ( Revised - 1983 ): Regulation 25 ( 2 ) Pursuant to section 22 ( 1 ) ( c ) ( ii ) of the Act , ventilation shall be considered to be adequate where the number of air changes every hour is ( a ) not less than ten in the case of processes which generate little or no heat , smoke or fume ; ( b ) not less than twenty in the case of processes which generate heat , smoke or fume . Provided that where any fume generated is likely to cause bodily injury to any person employed , the number of air changes every hour shall not be less than thirty .
CASE STUDY
Let us assume there is a job at Offshore Oil & Gas platform in Malaysia for Hot Work Repair ( e . g . welding and grinding ) in a Pressurised Vessel that is storing Hydrocarbon liquid , and the system is currently in operation mode with the configuration as shown below : a ) Depressurise the system by manipulating with the associated valves ( 1 ), ( 2 ) and ( 3 ). b ) Isolate the system by ensuring all upstream and downstream valves are closed . Bleed the remaining stored pressure ( 8 ) followed by Zero Energy confirmation via pressure gauges ( 5 ). c ) Install rated Blind Flanges at joint ( 5 - downstream ), ( 6 - upstream ) and ( 7 - downstream ). d ) Perform initial cleaning externally to remove the internal residue through with the following methods [ i ] Soaking ( Chemical Solvent ), [ ii ] Draining the content , [ iii ] Flushing with Water [ iv ] injecting Inert Purging Agent , and [ v ] Mechanical ventilation ( blower ). e ) Check the preliminary Atmospheric Gas reading in the Pressurized Vessel ( through joint 8 ) with the necessary respiratory PPE . Repeat the initial cleaning if necessary . f ) Set-up ventilation to achieve the Air Change in accordance to above legislation per the Nature of Work . Since welding fumes may be harmful to body ( Immediately Dangerous to Life or Health , IDLH ). Thus , the minimum Air Change needed is 30 air changes per hour .
● Find the Internal Volume of the Confined Space , let it be “ V ” in m 3
● Multiple the Internal Volume with the determined Air Change needed which is “ 30 V ”
● Divide the Air Change required in this case 30 V with the Blower capacity
1
6 8
5
4
2 3 7
5
57