Design for safety

System safety

System Safety is the application of engineering and management principles, criteria, and techniques to optimize all aspects of safety within the constraints of operational effectiveness, time, and cost throughout all phases of the system life cycle. It is a planned, disciplined and systematic approach to preventing or reducing accidents throughout the lifecycle of a system

Primary concern is the management of risks through:

  • Risk identification, evaluation, elimination & control through analysis, design & management

History of system safety

Design Safety arose in the 1950s after dissatisfaction with the fly-fix-fly approach to safety. Design Safety was first adopted by the US Air Force. It led to the development of mil-std-882 Standard Practice for System Safety (v1 1960s). The basic concept of System was rather than assigning a safety engineer to demonstrate that a design is safe, safety considerations were to be integrated from the design phase of the project.

Founding principles

Safety should be designed in

  • Critical reviews of the system design identify hazards that can be controlled by modifying the design
  • Modifications are most readily accepted during the early stages of design, development, and test
  • Previous design deficiencies can be corrected to prevent their recurrence

Inherent safety requires both engineering and management techniques to control the hazards of a system

  • A safety program must be planned and implemented such that safety analyses are integrated with other factors that impact management decisions

Safety requirements must be consistent with other program or design requirements

  • The evolution of a system design is a series of tradeoffs among competing disciplines to optimize relative contributions
  • Safety competes with other disciplines; it does not override them

The main principles of Safe design are:

  • Inherent safety
  • Safety factors
  • Multiple independent safety barriers

Inherently safe design 

Inherent: belonging to the very nature of the person/thing (inseparable). It is recommended that Inherent safe design should be the first step in safety engineering. Change the process to eliminate hazards, rather than accepting the hazards and developing add-on features to control them, unlike engineered features, inherent safety cannot be compromised.

Minimize inherent dangers as far as possible by considering the following:

  • Potential hazards are excluded rather than just enclosed or managed
  • Replace dangerous substances or reactions by less dangerous ones (instead of encapsulating the process)
  • Use fireproof materials instead of flammable ones (better than using flammable materials but keeping temperatures low)
  • Perform reactions at low temperatures & pressures instead of building resistant vessels

Safety Factors

Factors of safety (FoS), also known as safety factor (SF), is a term describing the load carrying capacity of a system beyond the expected or actual loads. Essentially, the factor of safety is how much stronger the system is than it usually needs to be for an intended load. Safety factors are often calculated using detailed analysis because comprehensive testing is impractical on many projects, such as bridges and buildings, but the structure’s ability to carry load must be determined to a reasonable accuracy.

When the material used is under strength, factor of safety covers uncertainties in material strength. It covers poor workmanship. It also covers unexpected behavior of the structure and natural disasters. Stresses are produced which may be very high. Factor of safety may take care of these loads during construction. Presence of residual stresses and stress concentrations beyond the level theoretically expected.

Multiple Independent Safety Barriers

Safety barriers are arranged in chains. The aim is to make each barrier independent of its predecessors so that if the first fails, then the second is still intact, etc. Typically, the first barriers are measures to prevent an accident, after which follow barriers that limit the consequences of an accident, and, finally, rescue services as the last resort.

The basic idea behind multiple barriers is that even if the first barrier is well constructed, it may fail, due to unforeseen reason, and that the second barrier should then provide protection. The major problem in the construction of safety barriers is how to make them as independent of each other as possible. If two or more barriers are sensitive to the same type of impact, then one and the same destructive force can get rid of all of them in one swoop.

These three principles of engineering safety – inherent safety, safety factors, and multiple barriers are quite different in nature, but they have one important trait in common. They all aim at protecting us not only against risks that can be assigned meaningful probability estimates, but also against dangers that cannot be probabilized, such as the possibility that some unforeseen even triggers a hazard that is seemingly under control. It remains, however, to investigate more in detail the principles underlying safety engineering and, not least, to clarify how they relate to other principles of engineering design.

 

 

Waste Minimization

Waste Minimization

Waste minimization is a practice or process through which the quantity of generated waste is reduced with the main objective of producing the least of unwanted by-products through the optimal use of raw materials, water and energy which in turn reduces the amount of waste entering the environment. It supports any company’s aim for a “Clean technology” production which means full utilization of resources, cost savings in storage, treatment & disposal of generated waste by reducing its volume and its strength or concentration, improves environmental compliance, ensures profit, and promote corporate good image.

For any company which is competing in today’s world, efficient and “clean” processes have become a necessity which not only involves maximization of all the resources and utilities, but also the minimization of waste products. This results in a more cost effective production and plant operation. This activity of waste minimization can be classified under Corporate Social Responsibility Activities and thus, greatly help in boosting a company’s reputation in the society due to which it should be one of the prime focal points for any company’s top management.

The process of waste management in a company can be initiated through the formation of a team/committee consisting of people within the company who are solely dedicated to reduction of waste management within the company. This team then conducts various audits to track the amount of waste being generated through various operations and accordingly comes up with a detailed plan to minimize it. This includes reduction in effluent production, cutting down costs by conservation of water & energy and even resource optimization to minimize wastage. These plans, once approved by the top management of the company, are communicated throughout the company and are encouraged to implement them for minimum waste generation. The progress in tracked through keeping a tab on the amount of waste being generated and comparing pre-implementation and post implementation waste generation and required improvements are made in the plan. This creates an efficient feedback loop for progress tracking and also helps with the enforcement of the plan.

Techniques for Efficient Waste Minimization:

Waste as defined (in the Local Order) is “any matter whether solid, liquid, gaseous or radioactive which is discharged, emitted or disposed in such volume or manner as to cause an alteration to the environment as well as any otherwise discarded, rejected, abandoned, unwanted or surplus matter that can be recycled, reprocessed, recovered or purified by a separate operation or process from that which was produced and even any matter prescribed to be waste and as defined by a competent department.” A waste, therefore, is an excess material resulting from any activities which is discharged as reject and unwanted or any surplus material whether as a total useless matter or those that can be rendered useful again by recycling, treatment or recovery thru a different process from which it was originally produced. Waste materials generated from manufacturing, processing & services from any industrial and commercial activities can be identified and grouped as follows:

  • Off-specification raw materials (contaminated, expired or outdated)
  • Off-specification spoiled products unfit for use or consumption
  • Contaminated products, including spills and leakages
  • Spent auxiliary materials (catalysts, solvents, filters, absorbents, etc.)
  • Undesirable by-products from maintenance activities (oils, solvents, etc.)
  • Undesirable products resulting from commissioning, start-up or process upset
  • Process waste water, including cooling & rinse water contaminated with chemicals
  • Air emission from the process, including fugitives & dust
  • Solid off-cuts, trimmings and excess materials
  • Used container & packaging materials

Ever since the Kyoto Protocol has been put into effect and widely accepted by countries all over the world, the organizations within these countries have become more vigilant about the emissions as well as managing the waste generated which in turn has led to a greater shift in focus for these organizations towards their CSR initiatives and has amplified the need of Waste Management tremendously.