Risk assessment was introduced and specifically addressed by the American National Standards Institute in ANSI B11.TR3:2000 entitled Risk assessment and risk reduction–A guide to estimate, evaluate, and reduce risks associated with machine tools. The ANSI B11.TR3 explored three major premises of risks:
- probability of occurrence—very likely, likely, unlikely, or remote
- severity of harm—catastrophic, serious, moderate, or minor
- exposure to hazard—frequency and duration, extent of exposure, or number of people exposed
ANSI B11.TR3 explains that zero risk does not exist and is therefore unattainable. Some amount of residual risk remains even after the application of machine safeguarding. ANSI’s organization of the B11 series of documents and technical reports can be visualized as a pyramid structure (see Diagram 1). ANSI defines three categories of safety standards:
- Type-A standards are BASIS standards. They give basic concepts, principles for design, and general aspects that can be applied to machinery. An example of a Type-A standard is the B11-2008 standard itself.
- Type-B standards are GENERIC standards. They deal with one or more safety aspects of one or more types of safeguards that can be used across a wide range of machinery. ANSI B11.19 on safeguarding methods is an example of a Type-B standard.
- Type-C standards are MACHINERY SAFETY standards. They deal with detailed safety requirements for a particular machine or group of machines. Examples of Type-C standards are ANSI B11.1 Mechanical Power Presses, ANSI B11.6 Lathes, ANSI B11.9 Grinders, and ANSI B11.15 Tube Benders.
The recently published ANSI B11-2008 General Safety Requirements Common to ANSI Machines falls under both Type-A and Type-B standards. and goes further into the subject of risk assessment for machinery, even though it is not mentioned in its title.
In the ANSI B11-2008 standard, “the expression ‘acceptable risk’ refers to the level at which further risk reduction will not result in significant reduction in risk; or additional expenditure of resources will not result in significant advantages of increased safety.” Achieving acceptable risk is the major point here. Risk reduction is considered complete when protective measures are applied and acceptable risk has been achieved for the identified hazards. At a minimum, this includes complying with local, regional, and national regulations.
ANSI B11-2008 also states that the user and the supplier may have different levels of acceptable risk and that a collaborative effort is required between the two to achieve that goal. It is noted that acceptable risk is fundamentally a business decision made by each supplier or user in the context of its own unique circumstances.
To minimize individual biases, a team approach is integral to assessing risk. This optimizes the combined judgment and expertise of individuals familiar with the tasks and hazards of a given machine tool. Four categories of risks are defined in ANSI B11-2008 as:
- high risk—only acceptable when all reasonable alternatives/options (protective measures) have been reviewed and deemed impractical or infeasible
- medium risk—undesirable but permissible when all reasonable alternatives/options (protective measures) have been formally reviewed and accepted by relevant stakeholders
- low risk—usually acceptable
- negligible risk—acceptable
ANSI B11-2008 compares the classical approach to risk reduction using the hazard control hierarchy to a more progressive approach to risk reduction based on two stages (see Diagram 2).
Stage one has two elements with a goal of eliminating the hazard(s) under analysis. Stage two has five elements that must be implemented in a balanced approach to reach the desired goal of reducing all remaining hazards or risks to an acceptable level. Clause 7 deals with specific risk reduction and safeguarding methods that contain the following 23 items:
- access to machine controls
- control systems
- electromagnetic compatibility (EMC)
- emergency stops
- control of hazardous energy (lockout/tagout)
- ergonomics/human factors
- handling of machines, component parts, and materials
- hydraulic and pneumatic (including vacuum) systems
- ladders and platforms
- machine tool systems
- modified atmospheres
- sanitation and hygiene
- thermal systems
- ventilation of airborne contaminants
In essence, the common primary objective in both ANSI B11.TR3 and ANSI B11-2008 is that reasonably foreseeable hazards must be identified and dealt with. Both standards contain scoring/rating systems to establish various risk reduction categories. ANSI B11.TR3:2000 and ANSI B11-2008 are available by visiting the Association of Manufacturing Technology or calling 703-893-2900.