FAULT TREE ANALYSIS (FTA)

-
The Fault tree analysis was first introduced at Bell laboratories by H.A. Watson 1962. It is one of the most widely used methods in system reliability,maintainability and safety analysis. It is a deductive procedure used to determine the various combinations of hardware, software failures and human errors that could cause  undesirable event.It is carried out to minimize and optimize resources.
     The deductive analysis begins with a general conclusion, then attempts to determine the specific causes of the conclusion by constructing a logic diagram called Fault Tree.
      So, Fault Tree is a logical model of the relationship of undesirable events to more basic events.The top level of the fault tree is the undesirable event. The middle events are intermediate events and the basic events are at the bottom.

                                           
The logic relationship of the events are shown by logic symbols or Gates.
The main purpose of the FTA is to help identify potential causes of system failures before the failures actually occur. It can also be used to evaluate the probability of the top event using analytical or statistical methods. These calculations involve system quantitative reliability and maintainability information such as failure probability, failure rate and repair rate. After completing FTA one can focus his efforts on improving system safety and reliability.

Fault tree construction

To do a comprehensive FTA, follow these steps:
  1. Define the fault condition, and write down the top level failure.
  2. Using technical information and professional judgments, determine the possible reasons for the failure to occur. Remember, these are level two elements because they fall just below the top level failure in the tree.
  3. Continue to break down each element with additional gates to lower levels. Consider the relationships between the elements to help you decide whether to use an "and" or an "or" logic gate.
  4. Finalize and review the complete diagram. The chain can only be terminated in a basic fault: human, hardware or software.
  5. If possible, evaluate the probability of occurrence for each of the lowest level elements and calculate the statistical probabilities from the bottom up.

Comments

Post a Comment

Popular posts from this blog

CRITICAL EQUIPMENT AND OPERATION UNDER ISM CODE.

-
Critical equipments are equipments whose failure will lead to a potential hazardous situation or an accident, thereby causing injury to personnel or loss of life or damage to marine environment or property. This causes deviation or failure of the ISM objective 1.2.2 of ISM code. PROVISION IN ISM :- Element 10.3 of ISM code states----      The company should establish procedures in its safety management system to identify equipment and technical system, the sudden operational failure of which may result in hazardous situation. The SMS should provide for specific measures aimed at promoting the reliability of such equipment or systems. These measures should include the regular testing of standby arrangement or equipment or technical systems that are not in continuous use.      Hence SMS must have with respect to the critical equipment have procedures:- 1) To identify them 2) To ensure their test and functional reliability 3) To establish and use the alternative arrangements on
Read more

Various codes of PSC inspection and how to present to PSCO in case IOPP equipment is not working

-
Following are the various codes which are used to represent Action to be taken by vessel against the deficiency reported:- Deficiency Action Codes 10 deficiency rectified 15 rectify deficiency at next port 16 rectify deficiency within 14 days 17 rectify deficiency before departure 18 rectify deficiency within 3 months  30 detainable deficiency 99 other (specify) Note: For ISM deficiencies, only code 10, 18 and 30 can be used. Restrictions on Updating Codes Both codes 15 and 16 can only be updated to code 10. Code 17 can only be updated to code 10, 15, 16 and 99. Code 18 can only be updated to code 10. Code 30 can only be updated to: - code 10 or 18 (ISM def.) - code 10 or 99 (non - ISM def.) Code 18 can only be updated to code 10. We will discuss one case where 15 ppm equipment has started malfunctioning just before the arrival of the port. After investigating it was found that the  coalescer filter has become very dirty and because of this th
Read more

CLEAR GROUND FOR DETAILED INSPECTION DURING PSC INSPECTION

-
CLEAR GROUNDS:- Evidence that the ship, its equipment or its crew does not correspond substantially with requirement of relevant convention or that the master or crew members are not familiar with essential shipboard procedures relating to the safety of ship or prevention of pollution.     Clear grounds to conduct a more detailed inspection include:- 1) The absence of principal equipment or arrangements required by convention :- e.g. MARPOL annex 1 requires that ship above 400 GRT and above must have an OWS with automatically stopping device, if effluent exceeds 15 ppm. Absence of this principal equipment will lead to detention. 2) Evidence from a review of the ship's certificate that it is clearly invalid: - e.g. Safety equipment certificate found invalid since no renewal survey was carried out. 3) Evidence that the ship's logs, manuals or other required documentation are not on board, are not maintained or falsely maintained:- e.g. ORB part 1 not present on board or in
Read more