High pressure hazards detection

COz is a nonflammable gas, therefore it does not present a tire or explosion hazard. The gas is generally considered toxic but will displace oxygen in the air, since it is 1.5 times heavier that air it wall settle and air supplies will be pushed out of the area. The CO2 gas is considered an asphyxiation hazard to personnel for this reason. Since the gas is odorless and colorless it cannot be easily detected by human observation in normal environments. Fire protection CO2 gas is normally stored under high pressure as a liquid and expands 350 times its liquid volume upon release. 

Compressed Air. Explosions have occurred in air compressors as a result of rapid oxidation of oil deposits in the piping between stages of multiple-stage compressors. Use of proper lubricants prevents deposition of oxidizable materials in high pressure piping (see LUBRICATION AND LUBRICANTS). High maintenance standards are required to detect and avoid the hazards associated with broken valves and other sources of hazardous recompression. 

The IPL must be capable of detecting and preventing or mitigating the consequences of specified, potentially hazardous event(s), such as a runaway reaction, loss of containment, or an explosion. A single IPL may address the multiple causes for that hazardous event and, therefore, multiple event scenarios may initiate action of one IPL. For example, high pressure in a vessel could be caused by either a pump dead-heading into it or by external fire. For both cases the vessel s pressure safety relief valve counts as a valid IPL. 

Problem A safety instrumented function is identified in a SRS. If a low liquid level is detected in a separation unit, the outlet valve must be closed to protect downstream equipment from high pressure blow-by which is the identified hazard. The inlet valve must also be closed, a pump must be turned off to avoid pump damage and the inlet valve for another process unit must be turned off to minimize process disruption. The logic for this function is given in a cause and effect diagram shown in Figure 7-3. What equipment is classified as primary versus auxiliary ... 

Safety instrumented systems (SIS) are frequently used in the oil and gas industry to detect the onsets of hazardous events (e.g., gas leakages and high pressures) and to mitigate their consequences to humans, the environment, and material assets. Failure to do so can lead to major accidents and it is therefore of vital importance to monitor the performance of the SIS in the operational phase. 

The hazardous event is initiated by the failure of either of the BPCS control valves when the reactor is at high pressure (>5 Barg). The scenario will result in a loss of containment due to overpressure of equipment in the gas processing unit. Due to the scenario risk, an SIL 1 SIF is proposed to detect high pressure and isolate the vent line. 

Perhaps, the most significant new term is Safety Instrumented Function (SIF). In ANSI/ISA-84.01-1996, there was very little differentiation between an SIS and SIF. ANSI/ISA-84.00.01-2004-1 spells out the difference between the SIF (e.g., hardware software used to mitigate a specific process risk) and the SIS (i.e., the hardware and software used to implement multiple SIFs). For example, consider a process furnace. If the main fuel gas pressure to the burner is too high, the flame may blow out, allowing uncombusted gases to be introduced into the furnace with the potential for a fire within the furnace. To prevent this hazard, an SIF is implemented in which block valves are used to isolate the main fuel gas from the process furnace when high fuel gas pressure is detected. These same main fuel gas valves may also be closed in response to low pilot gas pressure (i.e., a different process hazard). The SIS is the implementation of these two SIFs in the same logic solver. 

Optical detectors shall be used in more open configurations where pressure buildup due to the incipient explosion is limited. Optical detectors shall not be used where high dust concentrations limit the rehability of the suppression system. Both uv and ir detectors are available for optical detection. The use of daylight-sensitive sensors shall be avoided to avoid spurious activation. The sensor shall be mounted such that the angle of vision allows it to cover all the protected hazard area. The performance of an optical detector will also be affected by any obstacles within its vision, and this shall be overcome by the introduction of more detectors. Optical detectors shall be fitted with air shields to keep the optical lens clean. 

Vapor pressure and boiling point These two substance properties are also determining factors for flame. The lower the vapor pressure, the lower will be the hazard. In this case, a highly sensitive instmment will be required because lesser molecules may not be detected. The lesser the boiling, the more chances for evaporation, hence the more chance of a hazard. 

Toxicity of chemicals can be expressed in terms of IDLH (immediate danger to life and health) level, LCtso, REL (recommended exposure limit) and PEL (permissible exposure limit), and AEL (acceptable exposure Umit), among others. Physical and chenucal properties have direct influence on the behavior of a compound. For example, a vapor or liquid with high vapor pressure would create a respiratory inhalation hazard as the primary threat. Solids or low-volatility liquids may not produce a sufficieutly concentrated vapor to act as an inhalation threat. Their primary threat would be through direct contact. Specific hazards will dictate respective detection and evaluation methodologies. 

If highly toxic or flammable gases are stored inside without gas cabinets, they are usually required to be stored in a separate, gas storage room, where no other occupancies are permitted. This room should have its own ventilation, also directed to a gas treatment system that will abate any hazardous release. If pyrophoric gases are stored then smoke detection should be provided. The ventilation system must cause the pressure in the room to be less than atmospheric, to prevent any escape of gas from the room. The room should be constructed so that an explosion will be allowed to relieve pressure, usually in one direction, while the rest of the room structure remains intact. It is often required to have at least one cabinet on site, so that any leaking eylinders can be safely isolated. 

---