来自 昏昏睡睡HSE · From Drowsy HSE CSP DAILY LEARNING · DAY 178

FTA 与事件树 · 要点进阶 | Fault Tree & Event Tree · Key Points in Depth

第 35 块 · Domain 3 · 风险管理 · 15%Block 35 · Domain 3 · Risk Management · 15%第 2 / 5 课 · 要点进阶Lesson 2 of 5 · Key Points in Depth

本课只做一件事：把「FTA 与事件树」的四条要点逐条拆开：机制是什么、什么时候成立、最容易错在哪。

Take the four key points of Fault Tree & Event Tree apart: mechanism, conditions, and the usual misread.

本课不涉及：不重复概念定义，也不做综合题——只把要点讲透。
Not covered here: No repeat of definitions, no mixed questions — just the points, in depth.

先看一张图 | One picture first

向下拆门，向右排屏障——FTA 找组合致因，事件树评屏障 故障树 FTA（自顶向下） 顶事件：泄漏着火 OR 门（近似相加） 泄漏 0.01 垫片失效·腐蚀 点火源 0.02 静电·动火 OR ≈ 0.01+0.02 = 0.03；AND = 0.01×0.02 = 0.0002 最小割集 = 导致顶事件的最小基本事件组合 事件树 ETA（自左向右） 初始事件 泵密封失效 屏障 1 联锁停泵 屏障 2 围堰+喷淋 全部成功 → 安全 连续失败 → 事故 每过一道屏障，概率按其失效率打一次折； 结果谱从「安全」到「最坏可信」逐级展开。 OR 门相关性：支路共因时相加会低估
图解 / Figure：示意图（本站绘制，非官方图）/ Site-drawn diagram for study, not an official graphic.

本课目标 | Learning objectives

  1. 按顺序复述四条要点各自的机制
  2. 对每条要点说出一个常见误解，并说明为什么错
  3. 判断一个新例子属于哪一条要点

  • Recite the mechanism behind each of the four points
  • Name one common misread per point and why it fails
  • Classify a new example under the right point

    • 图片预览 / Photo preview

    图片经过压缩后保存在当前浏览器。导出失败时，可在下方预览图片上长按保存。/ The photo is compressed and stored in this browser. If download fails, long-press the preview below to save it.

    要点逐条拆 | Point by point

    1. AND 门相乘，OR 门相加
    AND multiplies, OR adds
    AND 门：P = P₁×P₂（都发生才行，概率变小）——例：0.01×0.02=0.0002。OR 门：P ≈ P₁+P₂（任一发生即可，概率变大）——例：0.01+0.02=0.03。设计含义：想降顶事件概率，把关键支路从 OR 改造成 AND（加独立屏障）最有效。
    AND: probabilities multiply, 0.01 times 0.02 equals 0.0002. OR: they roughly add, 0.01 plus 0.02 equals 0.03. Design meaning: to cut the top event, turn critical paths into AND logic by adding independent barriers.
    常见误解 / Common misread：误区：把「泵失效或阀失效」画成 AND。这等于宣称两个必须同时失效才漏——概率直接缩小百倍。
    Myth: drawing pump-or-valve as AND. That claims both must fail together and shrinks probability a hundredfold.
    2. 最小割集是树的「答案」
    The minimal cut set is the tree's answer
    割集＝一组同时发生就导致顶事件的基本事件；最小割集是去掉任何一个就不再成立的割集。一阶割集（单个事件直通顶事件）最危险——发现一阶割集要立即升级处理。分析优先级：先消灭一阶，再降二阶及以上。
    A cut set is a group of basic events that together produce the top event; a minimal cut set survives with nothing to remove. Order-one cut sets — a single event straight to the top — are the most dangerous and get escalated immediately. Kill order-one first, then work down.
    常见误解 / Common misread：误区：数门的数量评估风险。门多不代表安全，割集的阶数才说明结构性风险。
    Myth: count gates to judge risk. Cut-set order, not gate count, shows structural risk.
    3. OR 门的共因陷阱
    The common-cause trap under OR gates
    两条 OR 支路若共享同一电源、同一软件版本、同一操作员，就不独立——共同失效会同时触发两条支路，实际概率高于简单相加。处理：识别共因事件并在树里显式画出（把它挂到两支路共同的上游），或对共因单独加屏障。
    Two OR branches sharing a power supply, a software version or one operator are not independent — a shared failure triggers both and the real probability exceeds the naive sum. Draw the common cause upstream of both branches explicitly, or add a barrier against it.
    常见误解 / Common misread：误区：以为画了树就自动考虑了相关性。树只是模型，共因要分析者自己找出来。
    Myth: the tree reveals dependencies by itself. You find common causes; the tree records them.
    4. 事件树是屏障的考试
    An event tree is an exam for barriers
    从初始事件起，每道屏障两个分支（成功/失败），n 道屏障 2ⁿ 条路径；每条路径的概率=初始事件频率×各屏障成功/失败概率的连乘。读表要点：最后一线屏障失效的路径=最坏可信后果；「全部成功」路径的概率常被高估（屏障共因）。
    Each barrier branches success or failure, giving two-to-the-n paths; each path's probability is the initiating frequency times the products along it. Read the all-fail path as the worst credible outcome, and beware over-trusting the all-success path when barriers share causes.
    常见误解 / Common misread：误区：屏障画得越多越安心。屏障之间不独立（同一维护班组）时，多道屏障等于一道。
    Myth: more barriers mean more safety. Dependent barriers — one maintenance crew — act as one.

    情景自测 | Scenario check

    要点进阶Key points

    这道题考什么：考 AND/OR 概率近似。
    Tests AND/OR arithmetic.

    顶事件「气体泄漏着火」，两条 OR 支路：泄漏（0.01）与点火源（0.02）。近似顶事件概率？

    Top event gas leak fire has two OR branches: leak 0.01 and ignition 0.02. Approximate probability?

    自编练习题，不是 BCSP 官方真题，也不能用来预测分数。 / Original practice item, not an official BCSP exam question.

    动手练 | Practice

    1. 为一项作业画五栏事件树。
    Build a five-column event tree for one task.

    学习打卡与笔记 | Progress & notes

    已完成 0/4 项 / 0/4 tasks complete

    连续学习 / Learning streak: 0 天 / 0 days

    进度保存在当前浏览器，不会自动跨设备同步。/ Progress is stored in this browser only.

    PNG 学习记录预览；可长按图片保存 / PNG card preview; long-press to save

    可靠来源 | Official references

    BCSP — CSP Examination Blueprint (CSP11)

    BCSP — Official Self-Assessments

    BCSP — Certified Safety Professional (CSP)

    Pearson VUE — CSP 考试预约 / Scheduling

    本课为一般性学习资料，不替代现场专业评估、法规要求或组织程序。/ Educational content only.

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