Unsafe conditions

The job hazard analysis is a very important and effective process to determine hazardous conditions, unsafe practices, and system weaknesses. In this process the supervisor and an employee work together to analyze the specific task. The employee is observed performing the task. Next, they break the task down into steps. At this point, they jointly assess each step to identify any conditions and practices that might cause an injury/illness. Next, they work together on means and methods to eliminate those hazards. They revise procedures to make the task less hazardous. The supervisor, safety director, or safety committee should then take the process to its completion by uncovering the systems weaknesses related to the hazards found during the JHA. 

The first two factors are sometimes combined and simply referred to as unsafe conditions. Electrical accidents can be generally considered as being caused by rmsafe conditions, unsafe acts, or in what is usually the case, combinations of the two. 

When we inveshgate the loss, we can identify unsafe conditions, unsafe acts and lack of management controls and establish causes for these, as well as causes for the loss. Continuing the example ... 

Walls and Floor Openings Warning Devices Welding and Cutting Work Permit Working Surfaces Unsafe Conditions Unsafe Acts X-Rays... 

In fact, the basis of an audit is the assumption that its designer does indeed understand the process and has created an instrument to ensure that the process performs properly. Audits then, derive their content from the theory of accidents held by the author(s) of the audit. For example, depending on the author s point of view, the audit might emphasize unsafe conditions, unsafe acts, deficiencies in the safety-management system, or any number of other personally held accident-causation philosophies. 

An analysis is made of assessment findings to determine the nature and impact of hazardous conditions, unsafe practices, past history of losses, and at-risk events involved in the operation. 

Conclusion. The quantitative measurements, their interpretation, the calculated statistics, and the exposure criteria all come together to arrive at a conclusion to be drawn with a known chance of being wrong. The data and their interpretation give the extent of the conclusion. The exposure criteria, its origin and basis, define the impact of a conclusion that conditions are unsafe. 

Decision. Whereas a conclusion that conditions are to some degree unsafe requires that something be done, what should be done depends on the range and impact of the conclusion. The problem may be easy to correct, or it may no longer exist. The data may describe past conditions that do not presendy exist but may recur. It may be that the only possible decision is to undertake significant exposure reduction efforts at great cost. The possibiUty of each decision should have been anticipated when the evaluation was plarmed so that the data in hand support the decision that must be made. 

Process Safety Considerations. Unit optimization studies combined with dynamic simulations of the process may identify operating conditions that are unsafe regarding fire safety, equipment damage potential, and operating sensitivity. Several instances of fires and deflagrations in ethylene oxide production units have been reported in the past (160). These incidents have occurred in both the reaction cycle and ethylene oxide refining areas. Therefore, ethylene oxide units should always be designed to prevent the formation of explosive gas mixtures. 

Selective and Override Control When there are more controlled variables than manipulated variables, a common solution to this problem is to use a selector to choose the appropriate process variable from among a number of available measurements. Selec tors can be based on either multiple measurement points, multiple final control elements, or multiple controllers, as discussed below. Selectors are used to improve the control system performance as well as to protect equipment from unsafe operating conditions. 

Provide an aid to identify potential sources of unsafe conditions encountered in batch reaction systems. 

Incorrect electrical classification for equipment or auxiliary equipment, lighting, etc., possibly leading to unsafe conditions. 

It is worrying that a vessel which is safe when it enters service may become unsafe by slow crack growth - either by fatigue or by stress corrosion. If the consequences of catastrophic failure are very serious, then additional safety can be gained by designing the vessel so that it will leak before it breaks (like the partly inflated balloon of Chapter 13). Leaks are easy to detect, and a leaking vessel can be taken out of service and repaired. How do we formulate this leak-before-break condition ... 

There are a variety of ways of accomplishing a particular unit operation. Alternative types of process equipment have different inherently safer characteristics such as inventory, operating conditions, operating techniques, mechanical complexity, and forgiveness (i.e., the process/unit operation is inclined to move itself toward a safe region, rather than unsafe). For example, to complete a reaction step, the designer could select a continuous stirred tank reactor (CSTR), a small tubular reactor, or a distillation tower to process the reaction. 

We will not comment on why workers fail to report, but continue to believe that documentation of potential problems, unsafe conditions, and especially near misses (or more accurately referred to as near hits ) are important in the prevention of incidents at all types of sites. 

The TSE model of causation that accidents are primarily due to individually controllable unsafe acts is unlikely to be modified over time. This is because very little evidence on the background and conditions which led up to an accident will be collected. The data collection strategy is therefore likely to remain static, since the data collected wiU, by definition, not contradict the underlying assumptions. 

Indii iduals should immediately report any unsafe electrical conditions to prevent an accidental shock. Damaged or unauthorized extension cords must be taken out of service immediately. Indir iduals must shut off power at Uie breaker before disconnecting a damaged cord. To ensure Uiat someone else does... 

Individuals should immediately report any unsafe electrical conditions to prevent an accidental shock. 

Abnormally low pressure may not be an unsafe condition and the low-pressure switch may be automatic reset, closing again at a pressure corresponding to a temperature just below that of the load. 

Operation of the oil safety cut-out indicates an unsafe condition and such controls are made with hand reset switches. Normally open contacts on the switch can be used to operate an alarm to warn of the malfunction. 

However, since the suction gas to the compressor would then be hotter than its normal slightly superheated condition, the compressor may overheat and the discharge gas become too hot for correct and safe working. This form of capacity reduction is usually combined with a liquid injection valve, thermostatically operated, which introduces liquid also into the suction to keep it cool. The fitting of dual interdependent controls of this sort, both of which have inherent fail-unsafe possibilities, should be approached with caution. 

The checking and readjustment as necessary of all safety controls is an essential part of periodic maintenance - possibly annually. A time should be chosen when temporary stoppage of the plant will not cause inconvenience. Unsafe conditions can be set up by throtding valves, stopping pumps, or removing the load. In each case the relevant safety control should function at the pre-set conditions. Safety checks on specialized items such as fire dampers may be required from time to time by local authorities, and these checks, together with the expert advice available from the testing officers, should be welcomed as proof of the inherent safety of the installation. 

According to the AMC News article authorities summed up the report by pointing out that the incident was not the direct result of normal operations, but rather was the result of an unusual condition, and that the design and operating procedures were not unsafe when considered in the context of the total hazardous environment. The process in the nitration and purification building was operating normally when the rubber hose was introduced into the system. 

Most laboratories depend upon a steady supply of electric power, water, and gas. Very unsafe conditions may develop if any of these should fail, so precautionary measures must be taken. 

Maintenance is a never-ending task. Equipment manufacturers are normally very specific about periodic care of the products they sell, but many maintenance tasks are similar to those performed around the home. Minor repairs done in time will often prevent the development of unsafe conditions, as well as keep equipment in good working shape. 

An ignition experiment at 1-butene concentrations as high as 5% was performed to test instability in reaction behavior as an indication of unsafe operation (5% 1-butene in air 0.1 MPa 400 °C) [103]. The degree of conversion increased linearly and converged without any sign of instability. The power input corresponded to 6.5 W with an adiabatic temperature rise of more than 2000 °C. Plugging, however, was the major concern under these severe conditions. 

Clearly, the designer should always select a process that is inherently safe whenever it is practical, and economic, to do so. However, most chemical manufacturing processes are, to a greater or lesser extent, inherently unsafe, and dangerous situations can develop if the process conditions deviate from the design values. 

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