Pressure safety measures

Unfortunately, deaths occur every year in industry due to accidents that are preventable. Accidents are more likely to occur where firms are under pressure to meet targets, and safety measures tend to be ignored. The Health and Safety Executive (HSE) was set up to administer the Health and Safety at Work, etc. Act 1974 and incorporates... 

Section 38 of the Factories Act 1961 defines a steam boiler as a any closed vessel in which for any purpose steam is generated under pressure greater than atmospheric pressure . Economizers used to heat water being fed to such a vessel and superheater for heating steam are also included. Every boiler must be fitted with the recommended safety measures (e.g. safety valve, stop valve, water gauge, low-water alarms, pressure gages, etc.). 

The pressure is measured by means of a hydraulic system, either in one reference vessel of the 16-vessel rotor or simultaneously for all vessels of the 8-vessel rotor. The operational limit is 86 bar, sufficient for synthetic applications. In addition, a pressure rate limit is set to 3.0 bar s 1 by the control software provided. Protection against sudden pressure peaks is provided by metal safety disks incorporated into the vessel caps (safety limits of 70 bar or 120 bar, respectively) and by software regulations, depending on the rotor used and the vessel type. 

Precautions should be taken, especially in a scale-up approach, when dealing with exothermic reactions in the microwave field. Due to the rapid energy transfer of microwaves, any uncontrolled exothermic reaction is potentially hazardous (thermal runaway). Temperature increase and pressure rise may occur too rapidly for the instrument s safety measures and cause vessel rupture. 

A chemical engineer may have a choice of inherent safety variables, such as quantity stored or process temperatures and pressures, or process safety measures such as emergency isolation valves or containment systems, all of which may greatly reduce the vulnerabilities or the consequences of intentional loss. These are in addition to traditional security measures, which may include physical security, background checks, administrative controls, access controls, or other protective measures. For a more complete discussion of the options, refer to the AIChE Center for Chemical Process Safety Guidelines for Analyzing and Managing the Security Vulnerabilities of Fixed Chemical Sites and other references.f... 

Industry literature typically cites concern with open air explosions when 4,536 kgs (10,000 lbs.) or more of flammable gas is released, however, open air explosions at lower amounts of materials are not unheard of. When the release quantity is less than 4,536 kgs (10,000 lbs.), a flash fire is usually the result. The resulting fire or explosion damage can cripple a hydrocarbon processing facility. Extreme care must be taken to prevent the release of hydrocarbon from vessels resulting in vapor releases and resultant blast overpressure. Measures such as hydrotesting, weld inspections, pressure control valves, adequate pressure safety valves, etc., should all be prudently applied. 

The production of many silicone compounds makes use of substances which have a harmful effect on human body technological processes are often carried out at high temperatures and pressures. Therefore, safety measures are especially important. 

Risk evaluation programmes exist, for pressure vessels, which take into account European Directives [12] the risk factor - related to material brittleness and embrittlement, corrosion effects and localised stresses - is elevated and requires the adoption of rigorous safety measures. The manufacture and control procedures - including welding parameters and structural solutions - should be, in this case, more accurate and devoted to avoid the described defects. 

It has been suggested that, as an additional safety measure, methyl and ethyl azodicarboxylates be distilled at 0.1 -0.5 mm with a maximum oil bath temperature of 80°C. (S. C. Blackstock, Vanderbilt Department of Chemistry). Blackstock reports b.p 35-36oC/0.1 mm for dimethyl azodicarboxylate. Extreme care should be taken to maintain the pressure at or below that specified throughout the distillation. The receiver should be chilled in an ice bath. In addiiton, the drying step should be carried out very carefully since residual moisture will lead to hydrolysis during the distillation giving rise to diimide and carbon dioxide. 

In the case of Bhopal, water entered into pipes on the floor of the factory during routine cleaning but safety slips had not been placed at the joints. Water reached Tank E-610. The exothermic reaction between water and MIC increased the temperature of the tank converting liquid MIC into gas. The increase in pressure forced open the vent valve letting most of the MIC escape to the outside as gas. Various safety measures to neutralize MIC, such as caustic soda scrubbers, were not functional or unserviceable. Even if safety measures had been in perfect workig order, they could not have handled such a big leak. Fortunately, MIC stored in the other two tanks (E-611 and E-619) was not affected it was later converted to pesticide in what was... 

Double-wall tanks are known in various designs. In the simplest version an inner tank designed for storage temperature and pressure is surrounded by a second tank. The annular space between the two walls is filled with insulation material, for example, Perlite. The main purpose of the outer shell is to contain and hold the insulation. Today s usual practice is to design the outer shell to the same standard as the inner shell. This so-called double-integrity tank concept provides an additional safety measure as the outer tank can hold the full content if the inner shell fails. 

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