BS EN 746-3:2021 pdf free download – Industrial thermoprocessing equipment Part 3: Safety requirements for the generation and use of atmosphere gases.
Manual isolation valves shall be proven in the fully open position during operation. If it is proven automatically, then it shall meet the requirements of a protective system according to ISO 13577-4:2014. Automatic valves for emergency safety purge shall be normally open. Automatic valves for emergency shall have a manual by-pass valve piped in parallel.
When used, timers for purging shall comply with EN 60730-2-5:20 15, if applicable.
Purge gas supply pipework for fuel gas pipework/combustion chamber and purge of atmosphere gas pipework shall be securely isolated or shall not commonly be used.
4.3.2 Other safety devices
4.3.2.1 Trap seals
If a trap seal is used to contain combustible or toxic atmosphere, its performance shall be monitored. Any detected malfunction shall initiate a corrective procedure.
NOTE I Performance can be monitored with systems such as level sensors for liquids or gas warning systems for dry traps.
NOTE 2 Examples of corrective procedure may include audible alarms, automatic refill, shutdown, etc.
4.3.2.2 Safety devices for gas boosters/compressors
Where a gas booster/compressor is used, a low-pressure protection shall be fitted in the gas inlet system to the booster/compressor to ensure that depressurisation of upstream gas systems cannot occur. This low pressure protection shall cause shutdown of the booster/compressor in the event of reduced pressure and shall prevent automatic re-start on pressure restoration.
Gas pressure detectors shall comply with EN 1854:201013 or shall be evaluated to ensure appropriated reaction time and accuracy.
Attention shall be paid to the unintended decrease of atmosphere gas supply to the TPE which can result in unintended disability of maintaining positive pressure of TPE.
A suitable non-return valve shall be fitted between the booster/compressor outlet and the inlet to any storage vessel incorporated in the system.
The booster/compressor shall be fitted with a device to prevent the pressure from exceeding a predetermined safe value.
4.3.2.3 Devices for vacuum conditions
Where atmosphere gas or process liquids additions are supplied to TPE that are operating under, or may induce, a vacuum, then special consideration shall be given to the selection of any controls which can be subject to vacuum during both normal and abnormal conditions.
4.4 Requirements for the use of atmosphere gases
4.4.1 Prevention of potential ignitable atmospheres
4.4.1.1 General
If combustible atmosphere gases are used, the formation of ignitable atmospheres shall be avoided. The following subclauses detail established process requirements to avoid the formation of ignitable atmospheres inside a TPE.
The following methods shall be used, either singly or in combination.
4.4.1.2 Safety temperature
If for the safe operation of a TPE. the operating temperature shall be above the safe ignition temperature (750 °C), the temperature shall be monitored.
The start of admittance of the combustible atmosphere gas supply shall be interlocked with the safe ignition temperature. This function shall meet the requirements of a protective system according to ISO 13577-4:2014.
If the temperature in the TPE falls below the safe ignition temperature and a combustible atmosphere gas is used and a hazardous situation can occur, an alarm shall be caused. If this situation cannot be changed within a predetermined time, an emergency safety purge shall be performed (see 4.4.4). This function shall meet the requirements of a protective system according to ISO 13577-4:2014.