紧固器功能安全术语

2021年1月22日发(作者：contents)
基本术语

一、
IEC 61508
标准术语

说 明：以下术语摘录自功能安全标准
IEC61508
和国家标准
GB/T20438< br>。
4
。故术语标号也
未曾改动。


3.1
安全术语

3.1.1
伤害
harm
physical injury or damage to the health of people either directly or indirectly as a result of
damage to property or to the environment.
由于对财产或环境的破坏而导致的直接或间接地对人体健康的损害或对人身的损伤。

3.1.2
危险
hazard
potential source of harm
伤害的潜在根源

3.1.3
危险情况
hazardous situation
circumstance in which a person is exposed to hazard(s)
人暴露于危险的环境。

3.1.4


危险事件
hazardous event
hazardous situation which results in harm
导致伤害的危险情况。

3.1.5


风险
risk
combination of the probability of occurrence of harm and the severity of that harm
出现伤害的概率及该伤害严重性的组合。

3.1.6
允许风险
tolerable risk
risk which is accepted in a given context based on the current values of society
根据当今社会的水准
,
在给定的范围内能够接受的风险。

3.1.7
残余风险
residual risk
risk remaining after protective measures have been taken
采取防护措施以后仍存在的风险。

3.1.8
安全
safety
freedom from unacceptable risk
不存在不可接受的风险。

3.1.9
功能安全
functional safety
part of the overall safety relating to the EUC and the EUC control system which depends
on the correct functioning of the E/E/PE safety-related systems, other technology safety-r
elated systems and external risk reduction facilities
与
EUC
和
EUC
控制系统有关的整体安全的组成部分，
它取决于
E/E/PE
安全相关系统，
其
它技术安全相关系统和外部风险降低设施功能的正确行使。

3.1.10
安全状态
safe state
State of the EUC when safety is achieved
达到安全时
EUC
的状态。

3.1.11


合理的可预见的误用
reasonable foreseeable misuse
Use of a product, process or service under conditions or for purposes not intended by the
supplier, but which can happen, induced by the product, process or service in combinati
on with, or as a result of, common human behaviour
由于产品、
过程或服务加上人的行为习惯而导致的，
或者作为人的行为习惯的一个结果有可
能发生的，未按照供方要求的条件和用途对产品、过程和服务的 使用。






3.2
设备和装置
Equipment and devices
3.2.1
功能单元
functional unit
Entity of hardware or software, or both, capable of accomplishing a specified purpose
能够完成规定目的的软件、硬件或两者相结合的实体。

3.2.2
软件
software
intellectual creation comprising the programs, procedures, data, rules and any associated
documentation pertaining to the operation of a data processing system
包括程序、规程、数据、规则以及相关的数据处理系统操作文档在内的智能创作。

3.2.3
受控设备
equipment under control(EUC)
equipment, machinery, apparatus or plant used for manufacturing, process, transportatio
n, medical or other activities
用于制造、加工、运输、制药或其它活动的设备、机器、器械或成套装置。

3.2.4
EUC
风险
EUC risk
risk arising from the EUC or its interaction with the EUC control system
由
EUC
或由
EUC
与< br>EUC
控制系统相互作用而产生的风险。

3.2.5
可编程电子（
PE
）
programmable electronic
（
PE
）

可编程电子以计算机技术为基础， 可以由硬件、软件及其输入和
(
或
)
输出单元构成。

based on computer technology which may be comprised of hardware, software, and of in
put and/or output units
举例：下列均是可编程电子装置：

——
微处理器；

——
微控制器；

——
可编程控制器；

——
专用集成电路（
ASIC
）；

——
可编程逻辑控制器（
PLC
）；

——
其它以计算机为基础的装置（智能传感器、变送器、执行器）。

3.2.6
电气
/
电子
/
可编程电子

（
E/E/PE
）
electrical/electronic/programm able electronic
Based on electrical(E) and/or electronic(E) and/or programmable electronic (PE) technolo
gy
基于电气（
E
）和
/
或

电子（
E
）和
/
或

可编程电子（
PE
）的技术。

举例：电气
/
电子
/
可编程电子装置包括：

——
电－机装置（电气）；

——
使用电晶体的非可编程电子装置（电子）；

——
以计算机技术为基础的电子装置（可编程电子）

3.2.7
有限可变语言
limited variability language
Software programming language, either textual or graphical, for commercial and industria
l programmable electronic controllers with a range of capabilities limited to their applicatio
n
能力范围局限于应用的，用于工商业可编程电子控制器的，文本的或图形的软件编程语言。





3.3
系统：一般概念

3.3.1
系统
system
Set of elements which interact according to a design, where an element of a system can
be another system, called a subsystem, which may be a controlling system or a controlle
d system and may include hardware, software and human interaction
根据设计相 互作用的一组元素，
可能包括相互作用的硬件、
软件和人等。
系统中的某一元素
也可自成一个另外的系统，称为子系统，子系统可以是控制系统也可以是被控系统。

3.3.2
可编程电子系统
(PES) programmable electronic system(PES)
System for control, protection or monitoring based on one or more programmable electro
nic devices, including all elements of the system such as power supplies, sensors and ot
her input devices, data highways and other communication paths, and actuators and othe
r output devices
基于一个或多个可编程电子装置的控制、
防护或监视系统，
包括系统中所有的元素，
诸如电
源、传感器和其它输入装置，数据 高速公路和其它通信路径，以及执行器和其它输出装置

3.3.3
电气
/
电子
/
可编程电子系统

（
E/E /PES
）
electrical/electronic/programmable electronic system(E/E/PES)
System for control, protection or monitoring based on one or more electrical/electronic pr
ogrammable electronic (E/E/PE) devices, including all elements of the system such as po
wer supplies, sensors and other input devices, data highways and other communication p
aths, and actuators and other output devices.
基于一个或多个电气
/
电子
/
可 编程电子
(E/E/PE)
装置的用于控制、防护或监视的系统，包括
系统中所有的元 素
,
诸如电源、传感器和其它输入装置，数据高速公路和其它通信途径，以
及执行器和 其它输出装置

3.3.4
EUC
控制系统
EUC control system
System which responds to input signals from the process and/or from an operator and ge
nerates output signals causing the EUC to operate in the desired manner
对来自过程和
(或
)
操作者的输入信号起反应，产生能使
EUC
按要求的方式工作的输出 信号
的系统。

3.3.5
结构
architecture
Specific configuration of hardware and software elements in a system
在一个系统中硬件和软件元素的特定配置。

3.3.6
模块
module
Routine, discrete component or a functional set of encapsulated routines or discrete com
ponents belonging together
程序、分立部件、封装程序的一个功能集、或一组归并在一起的分立部件。

3.3.7
软件模块
software module
Construct that consists of procedures and/or data declarations and that can also interact
with other such constructs
由规程和（或）数据说明组成的构造，并能与其它这样的构造相互作用。

3.3.8
通道
channel
Element or group of elements that independently perform(s) a function
独立执行一个功能的一个或一组元素

3.3.9
多样性
diversity
different means of performing a required function
执行一个要求功能的不同方法。

3.3.10
冗余
redundancy
means, in addition to the means which would be sufficient, for a functional unit to perform
a required function or for data to represent information
对于执行一个要求功能的功能单元或对于表示信息的数据而言，除了够用之外还有多余。


3.4
系统：安全方面

3.4.1
安全相关系统
safety-related system
designated system that both:
implements the required safety functions necessary to achieve or maintain a safe state fo
r the EUC; and
—
is intended to achieve, on its own or with other E/E/PE safety-related systems, other te
chnology safety-related systems or external risk reduction facilities, the necessary safety
integrity for the required safety functions
所指的系统：

——
必需要能实现要求的安全功能以达到或保持
EU C
的安全状态；并且

——
自身或与其它
E/E/PE
安全 相关系统、
其它技术安全相关系统或外部风险降低设施一道
,
能够达到要求的安全功能 所需的安全完整性。

3.4.2
其它技术安全相关系统
other technology safety-related system
safety- related system based on a technology other than electrical/electronic/programmab
le electronic
基于电气
/
电子
/
可编程电子技术之外的安全相关系统。

3.4.3
外部风险降低设施
external risk reduction facility
measure to reduce or mitigate the risks which are separate and distinct from, and do not
use, E/E/PE safety-related systems or other technology safety-related systems
不使用
E/E/PE
安全相关系统或其它技术安全相关系统，
且与上述系统分开并不同的降低或减轻风险的手段。

3.4.4
简单
E/E/PE
安全相关系统
low complexity E/E/PE safety-related system
—
the failure modes of each individual component are well defined; and
—
the behaviour of the system under fault conditions can be completely determined
一种
E/E/PE
安全相关系统

其中：

——
已很好确定了每个单独部件的失效模式；

——
能完全确定在故障状况下系统的行为。

3.4.5
逻辑系统
logic system
Portion of a system that performs the function logic but excludes the sensors and final ele
ments
系统的一部分，用于执行功能逻辑，但不包括传感器和最终元件。


3.5
安全功能和安全完整性

3.5.1
安全功能
Safety function
function to be implemented by an E/E/PE safety-related system, other technology safety-
related system or external risk reduction facilities, which is intended to achieve or maintai
n a safe state for the EUC, in respect of a specific hazardous event
针对特定的危险事 件，为达到或保持
EUC
的安全状态，由
E/E/PE
安全相关系统、其它技
术安全相关系统或外部风险降低设施实现的功能

3.5.2
安全完整性
safety integrity
probability of a safety-related system satisfactorily performing the required safety function
s under all the stated conditions within a stated period of time
在规定的条件下、规定的时间内，安全相关系统成功实现所要求的安全功能的概率。

3.5.3
软件安全完整性
software safety integrity
measure that signifies the likelihood of software in a programmable electronic system ach
ieving its safety functions under all stated conditions within a stated period of time
在所有规定条件下和规定时间内表示软件在可编程电子 系统中执行其安全功能的可能性的
量值。

3.5.4
系统安全完整性
systematic safety integrity
part of the safety integrity of safety-related systems relating to systematic failures in a da
ngerous mode of failure
在危险失效模式中与系统失效有关的安全相关系统安全完整性的一部分


3.5.5
硬件安全完整性（
hardware safety integrity
）

part of the safety integrity of the safety related systems relating to random hardware failur
es in a dangerous mode of failure
在危险失效模式中与随机硬件失效有关的安全相关系统安全完整性的一部分。

3.5.6
安全完整性等级（
SIL
）
safety integrity level
（
SIL
）

discrete level (one out of a possible four) for specifying the safety integrity requirements o
f the safety functions to be allocated to the E/E/PE safety-related systems, where safety i
ntegrity level 4 has the highest level of safety integrity and safety integrity level 1 has the
lowest 一种离散的等级（四种可能等级之一），用于规定分配给
E/E/PE
安全相关系统的安全 功能
的安全完整性要求，在这里，安全完整性等级
4
是最高的，安全完整性等级
1
是最低的。

3.5.7
软件安全完整性等级
software safety integrity level
discrete level (one out of a possible four) for specifying the safety integrity of software in
a safety- related system
一种离散的等级（四种可能等级之一）用于规定在安全相关系统中软件的安全完整性。

3.5.8
安全要求规范
safety requirement specification
specification containing all the requirements of the safety functions that have to be perfor
med by the safety-related systems
一种技术规定，包括安全相关系统必须要执行安全功能的所有要求。

3.5.9
安全功能要求规范
safety function requirement specification
specification containing the requirements for the safety functions that have to be perform
ed by the safety-related systems
一种技术规定，包括安全相关系统必须要执行的安全功能要求。

3.5.10
安全完整性要求规范
safety integrity requirement specification
specification containing the safety integrity requirements of the safety functions that have
to be performed by the safety-related systems
一种技术规定，包括安全相关系统必须要执行的安全功能的安全完整性要求。

3.5.11
安全相关软件
safety-related software
software that is used to implement safety functions in a safety-related system
在安全相关系统中用于实现安全功能的软件。

3.5.12
操作模式
mode of operation
Way in which a safety-related system is intended to be used, with respect to the frequenc
y of demands made upon it, which may be either
-low demand mode: where the frequency of demands for operation made on a safety-rela
ted system is no greater than one per year and no greater than twice the proof- test frequ
ency
-high demand or continuous mode: where the frequency of demands for operation made
on a safety-related system is greater than one per year or greater than twice the proof- ch
eck frequency
——
低要求模式：
在这种模式下，
对一个安全相关系统提出操作要求的频率不大于每年一次
和不大于二倍的检验测试频率。
< br>——
高要求或连续模式：
在这种模式下，
对一个安全相关系统提出操作要求的频 率大于每年
一次或大于二倍的检验测试频率。

3.5.13
目标失效量
target failure measure
Intended probability of dangerous mode failures to be achieved in respect of the safety in
tegrity requirements, specified in terms of either
-the average probability of failure to perform the design function on demand (for a low de
mand mode of operation)
-the probability of a dangerous failure per hour (for a high demand or continuous mode of
operation)
相对于安全完整性要求要达到预计的危险模式失效概率，规定为下列两种之一：

——
按要求执行设计功能的平均失效概率（对于低要求操作模式）；

——
每小时危险失效的概率（对于高要求或连续操作模式）；

3.5.14
必要的风险降低
necessary risk reduction
risk reduction to be achieved by the E/E/PE safety- related systems, other technology saf
ety- related systems and external risk reduction facilities in order to ensure that the tolera
ble risk is not exceeded
为保证不超过允许风险， 由
E/E/PE
安全相关系统、其它技术安全相关系统和外部风险降低
设施达到的风险 降低。



3.6
故障、失效和错误

3.6.1
故障
fault
使功能单元执行要求之功能的能力降低或失去其能力的异常状况。

abnormal condition that may cause a reduction in, or loss of, the capability of a functional
unit to perform a required function
3.6.2
故障避免
fault avoidance
using techniques and procedures which aim to avoid the introduction of faults during any
phase of the safety lifecycle of the safety-related system
在安全相关系统安全生命周期的任何阶段中为避免发生故障而使用的技术和规程。

3.6.3
故障裕度
fault tolerance
the ability of a functional unit to continue to perform a required function in the presence of
faults or errors
在出现故障或错误的情况下，功能单元继续执行一个要求功能的能力。

3.6.4
失效
failure
the termination of the ability of a functional unit to perform a required function
功能单元执行一个要求功能之能力的终止。

3.6.5
随机硬件失效
random hardware failure
failure, occurring at a random time, which results from one or more of the possible degra
dation mechanisms in the hardware
在硬件中，由一种或几种机能退化可能产生的，按随机时间出现的失效。


3.6.6
系统失效
Systematic failure
failure related in a deterministic way to a certain cause, which can only be eliminated by
a modification of the design or of the manufacturing process, operational procedures, doc
umentation or other relevant factors
原因 确定的失效，只有对设计或制造过程、操作规程、文档或其它相关因素进行修改后，才
有可能排除这种失 效。

3.6.7
危险失效
dangerous failure
failure which has the potential to put the safety-related system in a hazardous or fail-to- fu
nction state
使安全相关系统处于潜在的危险或丧失功能状态的失效。

3.6.8
安全失效
safe failure
failure which does not have the potential to put the safety-related system in a hazardous
or fail-to-function state
不可能使安全相关系统处于潜在的危险或丧失功能状态的失效。

3.6.9
相关失效
dependent failure
failure whose probability cannot be expressed as the simple product of the unconditional
probabilities of the individual events which caused it
其概率不能表示为引起它的独立事件的无条件概率的简单乘积的失效。

3.6.10
共同原因失效
common cause failure
failure, which is the result of one or more events, causing coincident failures of two or mo
re separate channels in a multiple channel system, leading to system failure
一种失效，
它是一 个或多个事件导致的结果，
在多通道系统中引起两个或多个分离通道同时
失效，从而导致系统失 效。

3.6.11
错误
error
discrepancy between a computed, observed or measured value or condition and the true,
specified or theoretically correct value or condition
计算、观测和测量到的值或条件与真值、规定的或理论上的正确值或条件的差异。

3.6.12
人为错误
human error
失误
mistake
human action or inaction that produces an unintended result
引发非期望结果的人的动作或不动作


3.7
生命周期活动

3.7.1
安全生命周期
safety lifecycle
necessary activities involved in the implementation of safety-related systems, occurring d
uring a period of time that starts at the concept phase of a project and finishes when all of
the E/E/PE safety-related systems, other technology safety-related systems and external
risk reduction facilities are no longer available for use
安全相关系统实现过程中所必需的生命活动，这 些活动发生在从一项工程的概念阶段开始，
直至所有的
E/E/PE
安全相关系统，其 它技术安全相关系统，以及外部风险降低设施停止使
用为止的一段时间内。

3.7.2
软件生命周期
software lifecycle
activities occurring during a period of time that starts when software is conceived and end
s when the software is permanently disused
从软件开始构思到软件永久停用期间的活动。

3.7.3
配置管理
configuration management
discipline of identifying the components of an evolving system for the purposes of controll
ing changes to those components and maintaining continuity and traceability throughout t
he lifecycle
为了控制系统部件的改变和在生命周期全过程中保持连续性和可 追溯性，
标记一个进化中的
系统部件的规则。

3.7.4
影响分析
impact analysis
activity of determining the effect that a change to a function or component in a system will
have to other functions or components in that system as well as to other systems
确定一个系统中的一个功能或部件的改变将对该系统中其它功能或 部件以及其它系统产生
影响的活动。


3.8
安全量的证实

3.8.1
验证
verification
confirmation by examination and provision of objective evidence that the requirements ha
ve been fulfilled
通过检查和提供客观证据证实规定要求已经满足。


3.8.2
确认
validation
confirmation by examination and provision of objective evidence that the particular requir
ements for a specific intended use are fulfilled
通过检查和提供客观证据来证明某一特定预期用途的特殊要求已经满足。

3.8.3
功能安全评估
functional safety assessment
investigation, based on evidence, to judge the functional safety achieved by one or more
E/E/PE safety-related systems, other technology safety-related systems or external risk r
eduction facilities
通过调查，依据证据来判断一个或多个
E/E/PE
安全相关系统、其它技术安全相关系统或外
部风险降低设施达到的功能安全。
3.8.4
功能安全审核
functional safety audit
systematic and independent examination to determine whether the procedures specific to
the functional safety requirements comply with the planned arrangements, are implemen
ted effectively and are suitable to achieve the specified objectives
对于按计划安排的功能安全要求专用的规范是否有效地执 行并满意地达到规定目的进行系
统地、独立的检查。

3.8.5
检验测试
proof test
periodic test performed to detect failures in a safety-related system so that, if necessary, t
he system can be restored to an
―as

new‖
condition or as close as practical to this conditi
on
用以检测安全相关系统失效的周期性测试，
在必要时可把系统复 原到正常状态或实际上接近
正常的状态。


3.8.6
诊断覆盖率
diagnostic coverage
fractional decrease in the probability of dangerous hardware failure resulting from the ope
ration of the automatic diagnostic tests
进行自动诊断测试而导致的硬件危险失效概率的降低部分。

3.8.7
诊断测试间隔
diagnostic test interval
interval between on-line tests to detect faults in a safety-related system that have a specif
ied diagnostic coverage
在一个已经规定了诊断覆盖的安全相关系统中，为检测故障而进行的在线测试的间隔。

3.8.8
检测到的
detected
Detected
revealed overt
in relation to hardware, detected by the diagnostic tests, proof tests, operator intervention
(for example physical inspection and manual tests), or through normal operation
揭露出的

明显的

与硬件相关，用诊断测试 、检验测试、操作员干预（如设备检测和人工测试）或通过正常操
作所发现的。

3.8.9
未检测到的
undetected
未揭露的
unrevealed
不明显的
covert
in relation to hardware, undetected by the diagnostic tests, proof tests, operator interventi
on (for example physical inspection and manual tests), or through normal operation
与硬件有关，用诊断测试、检验测试、操作员干 预（如设备检测和人工测试）或通过正常操
作未发现的。

3.8.10
无关人员
independent person
Person who is separate and distinct from the activities which take place during the specifi
c phase of the overall, E/E/PES or software safety lifecycle that is subject to the functiona
l safety assessment or validation, and does not have responsibility for those activities
与整体的、
E/E/PES
的或软件的 安全生命周期特定阶段中的活动无关，并且不对其直接负
责，但又从事功能安全评估或确认的人。

3.8.11
无关部门
independent department
Department which is separate and distinct from the department responsible for the activiti
es which take place during the specific phase of the overall, E/E/PES or software safety li
fecycle that is subject to the functional safety assessment or validation
与整体的、
E/E/PES
的 或软件的安全生命周期特定阶段中的活动无关，并且不对其直接负
责，但又从事功能安全评估或确认的部 门。

3.8.12
无关组织
independent organization
Organization which is separate and distinct, by management and other resources, from t
he organizations responsible for the activities which take place during the specific phase
of the overall, E/E/PES or software safety lifecycle that is subject to the functional safety
assessment or vaildation
与整体的、
E /E/PES
的或软件的安全生命周期特定阶段中的活动无关，并且不对其直接负
责，但又从事 功能安全评估或确认的组织。

3.8.13
动画
animation
Simulated operation of the software system (or of some significant portion of the system)
to display significant aspects of the behaviour of the system, for instance applied to a req
uirements specification in an appropriate format or an appropriate high-level representati
on of the system design
软件系统（或 系统的某一重要部分）
的动画，
以显示系统行为的主要面貌，
例如适用于适当
格式的要求规范或系统设计的高级表述。

3.8.14
动态测试
dynamic testing
Executing software and/or operating hardware in a controlled and systematic way, so as t
o demonstrate the presence of the required behaviour and the absence of unwanted beh
aviour
用系统的和受控的方式执行软件和
（或）
操作硬件以证 明所要求的行为的存在以及非要求行
为的不存在。

3.8.15
测试装置
test harness
Facility that is capable of simulating (to some useful degree) the operating environment o
f software or hardware under development, by applying test cases to the software and re
cording the response
在开发阶段能 够仿真软件或硬件操作环境的装置。
通过把测试实例应用于软件，
能够模拟
(
达
到某个可用的程度
)
开发中的软件或硬件的操作环境并记录响应的设施。



二、
IEC61511
标准术语

说明：以下术语摘录自
IEC61511
标准和相关的标准翻译稿，
其中有一些术语在前 面出现过，
但表述略有不同，差别反映了过程控制领域的习惯与特殊性。

3.2.1
结构
architecture
Arrangement of hardware and/or software elements in a system, for example
(1) arrangement of safety instrumented system (SIS) subsystems
(2) internal structure of an SIS subsystem
(3) arrangement of software programs
系统中硬件和
/
或软件元素的安排，如：

（
1
）安全仪表系统（
SIS
）子系统的安排；

（
2
）
SIS
子系统的内部结构；

（
3
）软件程序的安排。

3.2.2
资产保护
asset protection
Function allocated to system design for the purpose of preventing loss to assets
为防止资产损失分配给系统设计的功能。

3.2.3
基本过程控制系统（
BPCS
）
basic process control system
（
BPCS
）

System which responds to input signals form the process, its associated equipment, othe
r programmable systems and/or an operator and generates output signals causing the pr
ocess and its associated equipment to operate in the desired manner but which does not
perform any safety instrumented functions with a claimed
SIL≥1

对来自过程的、
系统相关设备的、其他可编程系统的和
/
或某个操作员的输入信号进行响应，
并产生使过程和系统相关设备按要求方式运行的系统，但它并不执行任何具有被声明的
SIL≥1
的仪表安全功能。

3.2.4
通道
channel
element or group of elements that independently perform(s) a function
独立执行一个功能的一个或一组元素。

3.2.5
编码
coding
3.2.6.1
共同原因失效
common cause failure
failure, which is the result of one or more events, causing failures of two or more separat
e channels in a multiple channel system, leading to system failure
由一个或多个事件引起一个 多通道系统中的两个或多个分离通道失效，
从而导致系统失效的
一种失效。

3.2.6.2
共同模式失效
common mode failure
failure of two or more channels in the same way, causing the same erroneous result
两个或多个通道以同样的方式引起相同的误差结果的失效。

3.2.7
部件
component
one of the parts of a system, subsystem, or device performing a specific function
执行某一特定功能的系统、子系统或装置的一个组成部分。

3.2.8
配置
configuration

3.2.9
配置管理
configuration management
discipline of identifying the components of an evolving (hardware and software) system fo
r the purpose of controlling changes to those components and maintaining continuity and
traceability throughout the life cycle
为了在 生命周期全过程中控制组件的变化
（硬件和软件）
和保持连续性和可追溯性，
对进化< br>系统（硬件和软件）中组件的识别规则。

3.2.10
控制系统
control system
system which responds to input signals from the process and/or from an operator and ge
nerates output signals causing the process to operate in the desired manner
对来自过程 和
/
或操作员的输入信号进行响应，并产生使过程按要求方式运行的输出信号的
系统。

3.2.11
危险失效
dangerous failure
failure which has the potential to put the safety instrumented system in a hazardous or fai