1. SCOPE
2. REFERENCES
3. DEFINITIONS
4. GENERAL
5. DESIGN
- General
- Reactor
- Distillation Systems
- Heat Transfer Equipment
6. SUBSTITUTION / ELIMINATION
7. ATTENUATION / MODERATION
- General
8. LIMITATION OF EFFECTS
- General
- Batch Reactors
- Limiting the Possible Magnitude of Process Deviations
- Transport
- Limitation for Personnel Exposure
9. SIMPLIFICATION / ERROR TOLERANCE
- General
- Containment Within Process Equipment
- Optimization/Simplification of Instrumentation and Interlocks
- Piping
10. HUMAN FACTORS
- Ergonomics
- Interaction of Personnel with Equipment, Controls, and the Work Environment
11. INCORPORATING SAFE DESIGN CONCEPT IN PROCESS HAZARD ANALYSIS
12. PLANT LAYOUT AND FACILITY SITING
TABLE I Inherently Safer Design Review Checklist
TABLE II Ergonomics Review
TABLE III Chemical Interaction Matrix
1. Scope
This standard is for new facilities and process equipment, that allows the design of the process, plant, and equipment so that they are inherently safer, with emphasis on major hazard plants. Electrical safety is not within the scope of this standard.
2. References
SABIC Engineering Standards
S01-G01 Safety Considerations for Plant Layout
3. Definitions
Attenuation. Using less hazardous conditions or a less hazardous form of a material.
Ergonomics. Science that coordinates the design of devices, systems, and physical working conditions with the capacities and requirements of the worker.
Highly toxic materials (HTMs). Those substances that, because of their toxic and physical properties, pose a significant hazard to persons off-site if accidentally released. Typically, highly toxic materials have a substance hazard index greater than 4000. See SES S21 -G01 for more information.
Inherently Safer Design. A design that relies chemistry and physics – the quantity, properties, and conditions of use of the process materials – to prevent injuries, environmental damage and property damage rather than on control systems, interlocks, alarms and procedures to stop incipient incidents.
Intensification. Using small quantities of hazardous substances.
Limitation of Effects. Designing facilities that make operating errors less likely, and that are forgiving of errors that are made.
Substitution. Replacing a material with a less hazardous substance.
4. General
4.1 One of the principal ways in which a process may be made inherently safer is to limit the inventory of hazardous material. The design philosophy shall be to minimize the volume of process chemicals required, saving on both the cost of vessels and of supporting structures.
4.2 Storage of hazardous and highly toxic feedstock, intermediates, and products shall be kept to minimum quantities. Alternate methods of storage and potential for elimination of intermediate storage shall be evaluated.
5. Design
5.1 General
5.1.1 A principal route to limitation of inventory is intensification of the process. Consideration shall be given to carrying out the reactions or unit operations using small volumes. Process intensification shall be considered for reactors, mass transfer operations such as distillation and gas absorption, heat exchange, steam reforming.
5.1.2 A review shall be conducted to keep to a minimum sources of leaks, for example, agitators, pumps, external coolers and connecting pipework. The following shall be evaluated for strategies to reduce inventories:
a. Raw materials
b. Intermediates
c. Finished products
d. Storage
e. Equipment design
f. Process conditions
g. Transfer and transport
5.2 Reactors
5.2.1 Reactors often present a large portion of the inventory of hazardous material in a chemical process. With a thorough understanding of the reaction, the designer can identify reactor configurations that maximize yield and minimize size, resulting in a more economical process, reducing generation of by-products and waste, and increasing inherent safety by reducing the reactor size and inventories of all materials.
5.2.2 Consideration shall be given to the potential for the use of high intensity mixing devices such as pipes, nozzles and pumps as reactors, and where applicable, the application of power fluidics technology to the design of a range of mixers and reactors. Long, small diameter pipe used as a reactor reduces hazards in that in the event of a rupture the rate of release would be low, and isolation by emergency isolation valves relatively simple.
5.3 Distillation Systems
The following should be considered for inventory reduction in conventional distillation systems: Minimize the size of reflux accumulators and reboilers
a. Use internal reflux condensers and reboilers where practical
b. Use column internals that minimize holdup without sacrificing operation efficiency
c. Reduce the amount of material in the base of the column by reducing the diameter of the base
d. Remove toxic, corrosive, or otherwise hazardous materials early in a distillation sequence, reducing the spread of such materials throughout a process
e. Use low-inventory distillation equipment such as the thin film evaporator for hazardous materials, reactive or unstable materials
5.4 Heat Transfer Equipment
Heat transfer equipment has a great variation in heat transfer area per unit of material volume. Process inventory can be minimized by using heat exchangers with the minimum volume of hazardous process fluid for the heat transfer area required. Plate heat exchanger technology goes beyond conventional heat transfer by coating the plates with catalyst, creating a plate heat exchanger reformer, reducing the size of conventional reforming vessels.
6. Substitution / Elimination
6.1 The starting point for inherently safer design is the selection of the process, the objective being to choose a process that eliminates particularly hazardous chemicals, or operates under less hazardous conditions, but if both criteria can be met, that wil be the best design. Processes shall be reviewed and consideration given to the feasibility of substituting less hazardous features for hazardous ones. Inherent safety of the manufacturing process for a material can be greatly increased by development of alternate chemistry.
6.2 The following shall be considered and strategies developed for improving the process design where applicable:
a. Alternative chemistry or processes
b. Substitution of chemicals
c. Utilities
6.3 Areas where substitution is often effective include heat transfer media, solvents, and chlorine manufacturing processes. Consideration should be given to replacing volatile organic solvents with aqueous systems or less hazardous organic materials.
6.4 Catalysts should be reviewed for identification of catalysts that enhance reaction selectivity or allow the desired reaction to be carried out at a lower temperature or pressure, developing inherently safer chemical synthesis routes that are Polymer supported reagents, catalysts, protecting groups and mediators can be used in place of small molecule materials, making intermediate materials that are toxic, noxious, or corrosive safer.
7. Attenuation / Moderation
7.1 General
7.1.1 Attenuation involves the use of less hazardous process conditions. This can be accomplished by strategies that are either physical (lower temperatures, dilution) or chemical (development of a reaction chemistry that operates at less severe conditions).
7.1.2 What constitutes a less hazardous process condition is not always obvious and shall be reviewed carefully, as the issues are multi-dimensional and impacts often difficult to determine. A compromise solution may turn out to be the most hazardous. The hazard may be relatively low for a process with a large inventory but operating at low pressure and temperature such that if an escape occurs only a small amount of material will flash off. At the other extreme, a process operating at high temperature and pressure may present only a low hazard, because the use of these operating conditions allows the inventory to be kept low.
The compromise solution of moderate inventory at moderate pressure and temperature may actually be the most hazardous, if the conditions are such that on release a large fraction of the material will flash off and the inventory is such that the quantity esca ping is likely to be large.
7.1.3 Areas that often benefit from attenuation/moderation reviews include liquefied gases, explosive powders, and runaway reactants. Use of a higher boiling solvent may reduce the normal operating pressure of a process and will also reduce the maximum pressure resulting from an uncontrolled or runaway reaction. The process shall be reviewed thoroughly for opportunities to reduce inherent hazards by considering the following:
a. Reaction conditions
b. Catalyst
c. Design parameters
d. Dilution of raw materials to a less hazardous state
e. Refrigeration systems for storing at or below the atmospheric boiling point.
7.1.4 Consideration shall be given to reducing holdup inventory by reviewing the following for potential application:
a. Using a narrow bottom section design for columns
b. Using thermosiphon reboilers as opposed to kettle reboilers.
c. Eliminating intermediate storage.
8. Limitation of Effects
8.1 General
The process shall be evaluated to ensure the design is not only under designed, but also overdesigned. For example, limitation of items such as pump size or valve trim in order to prevent overpressure of the plant is a valid method of achieving inherently safer design, but where it is used it is necessary to ensure that the design intention is not defeated by installation of oversized items either at initial construction or subsequently.
8.2 Batch Reactors
Semi-batch or gradual addition batch processes shall be considered to limit the supply of one or more reactants. On-line heat balance and monitoring of the temperature gradient shall be considered as a method to confirm that the limiting reactant is being consumed.
8.3 Limiting the Possible Magnitude of Process Deviations
Process equipment shall be reviewed and designed to limit the size of possible deviations from desired operating conditions by considering the following:
a. Limiting the rate of addition of a material to a process vessel by selecting a pump with a maximum capacity lower than the safe rate of addition for the process
b. For material fed by gravity, limiting the maximum feed rate by sizing the feed pipe such that the maximum possible flow is within safe limits
c. Pump and pipe sizing is preferred or the use of restriction orifices as the latter can corrode/errode or be inadvertently left out of the line
d. Limiting total charge to a reactor by limiting the capacity of pre-charge or feed tank capacity e. Use three way valves on charge tanks to make it nearly impossible to transfer material directly from storage to a reactor
f. For reactors with existing charge tanks which are larger than are needed, reduce the effective capacity of the tank by providing overflow at the appropriate level in the tank
g. Optimize heat transfer for the required task by selecting a heat transfer media that limits the maximum or minimum temperature attainable in a vessel
h. For materials that require heating but may become unstable if overheated, design the heating system to minimize the potential for overheating in the event of failure of the tank temperature control system
i. Select materials of construction including piping selection, corrosion allowances, gasket types for compatibility with process streams
j. Process interlocks
k. Non-return valves
8.4 Transport
8.4.1 Consideration shall be given to using miniaturized on-site production plants that can produce on a ‘just-in-time’ basis, eliminating the need for transport of hazardous chemicals and for eliminating storage inventory. Opportunities for on-site production exist if the production and operating states match requirements, but require change for transport, requiring additional hazardous process steps after transport. For example, aqueous HF is produced and used in a dilute state, but normally concentrated for transport. Other opportunities may exist with molten polymers, liquefied gases, and many powders. Cost benefit analysis shall be applied to consider requirements for automation and reliability to address business interruption issues associated with a ‘just-in-time’ production basis.
8.4.2 Feedstock and utility requirements shall be evaluated for availability from other processes on site to eliminate the need for transport. Examples of utilities that are often available are air, methane, water, electricity.
8.5 Limitation for Personnel Exposure
8.5.1 Limitation of exposure of personnel shall be achieved by location of the workbase and by control of access to high hazard zones. SES S01-G01, Safety Considerations For Plant Layout, states requirements for facility siting, unit and equipment layout and spacing, and locations of control rooms.
8.5.2 Handling solids in the form of larger particle size granules or pellets rather than a fine powder reduces the potential for worker exposure, and if the solid is combustible, the dust explosion hazard can be reduced or eliminated as well. Worker exposure hazards can also be reduced by formulating dyes as liquids or wet pastes rather than dry solids or powders.
9. Simplification / Error Tolerance
9.1 General
A fundamental principle of inherently safer design is simplicity. Aspects of simpler design include:
a. Design for full overpressure
b. Design modification to avoid instrumentation
c. Use of resistant materials of construction
d. Use of simple alternatives to instrumentation
e. Design for critical temperature
9.2 Containment Within Process Equipment
Consideration shall be given to the following:
a. Designing vessels to withstand the maximum overpressure resulting from a process incident as an alternative to the provision of a pressure relief system
b. Designing equipment strong enough to contain the maximum pressure resulting from a deflagration of a combustible organic dust or flammable organic vapor in air
c. Designing vessels for full vacuum
d. Choosing a reactor design pressure sufficiently high to contain the maximum pressure resulting from a runaway reaction eliminating the need for a large emergency relief system
e. For cases where it is not feasible to contain a runaway reaction within the reactor, consider piping the emergency relief device effluent to a separate pressure vessel for containment and
subsequent treatment
f. Design shell and tube side of heat exchangers to contain the maximum attainable pressure, eliminating the need for pressure relief to protect the exchanger shell in case of tube rupture
g. Separating multistep batch processes and complicated systems into several vessels each optimized for a single processing step, simplifying the interactions between process fluid and utilities
h. Identify the safest failure position for all electric or pneumatic valves and verify in the process hazard analysis by considering all possible failure positions
9.3 Optimization/Simplification of Instrumentation and Interlocks
The following shall be considered for instrumentation and interlocks:
9.4 Piping
a. Providing alternative designs that reduce or eliminate the need for instrumentation
b. Using more resistant materials to eliminate the need for installing instruments that are used for prevention of attack on materials of construction
c. Where a control function is to be carried out, simple alternatives to instrumentation should be considered. For example, level control may be effected by a stand-pipe
d. Through the assignment of inputs or outputs, the DCS systems shall be designed in such a manner as to prevent simultaneously disabling a large number of control loops upon failure of a module.
The following inherently safer design principles shall be considered for piping designs:
a. Piping systems shall be designed to minimize the use of components that are prone to leak or fail
b. Sight glasses shall be eliminated wherever possible
c. Piping shall be designed to eliminate the need for flexible connections
d. Welded pipe is preferred over flanged piping
e. Threaded piping shall be avoided for flammable and toxic materials
10. Human Factors
10.1 Ergonomics
10.1.1 Ergonomic principles shall be considered in the design of all facilities by all functions. The ergonomic strategy shall be to design the facilities correctly rather than try to correct problems after construction. Facilities shall be designed to accommodate males and females of all ages.
10.1.2 Design strategies to eliminate injury shall be considered for all human interfaces in the following ergonomic categories:
a. Physical size
b. Endurance
c. Force
d. Hand and Arm Usage
e. Environment
f. Information Processing
10.1.3 Workspace design shall be compatible with anthropometric data for 5 percentile female and 95 percentile male.
10.2 Interaction of Personnel with Equipment, Controls, and the Work Environment
The following Human Factors issues shall be reviewed and included in where applicable in the design:
a. Coordination of information – integrated system for data gathering, consistency in display and control conventions, prioritization of displays, exceptions to normal response, decision aids, communication network, information required by operators during emergency situations
b. Materials handling – acute and chronic strain, storage area layout, rack design, mechanical lifting
c. Equipment design – location, displays, labels, control access, accidental activation, interlocks, maintenance access,
d. Equipment naming, labeling, panel arrangement, and field operator interface details (utility stations, manual alarm call point, etc.) to be consistent with operating standards and behavior patterns.
e. Location accessibility, and isolation of high pressure components that pose special risk during maintenance of emergency recovery from component failure
11. Incorporating Safe Design Concept in Process Hazard Analysis
11.1 An Inherently Safer Design Review using the checklists in Table 1 as a guideline shall be conducted as early in the project as possible, preferably initiated in the conceptual design stage, to gain the most benefit and cost savings. The review process utilizes the following tools:
a. Brainstorming with a degree of structure
b. Review of flow sheets and process diagrams
c. Examination using checklists
11.2 As a part of the review process, the chemical interaction matrix (Table 3), shall be used to identify potential chemical incompatibilities, storage requirements in regards to separation of reactive chemicals, and design issues.
11.3 An Ergonomic Design Review using the procedure outlined in Table 2 shall be completed either as a sub task of the Process Hazards Analysis, or as a separate activity.
12. Plant Layout and Facility Siting
See SES S01-G01, Safety Considerations for Plant Layout shall be followed.
Table I – Inherently Safer Design Review Checklist
Table II – Ergonomics Review
Planning and Objectives
The review team is expected to perform the following tasks:
a. Review project ergonomic principles
b. Review ergonomics systems, design ramifications, and effects
c. Process task list
(i) Identify missing tasks
(ii) Gain agreement on who would perform task
(iii) Identify any ergonomic concerns associated with the task by discussing its relationship to the six ergonomic systems and the project ergonomic principles.
(iv) Highlight areas of concern for future action
d. Perform Expanded Analysis for tasks requiring additional attention.
This ergonomics review shall be conducted according to the following agenda which is consistent with the expectations stated above:
a. Introduction
b. Review of Ergonomics Principles
c. Review ergonomic systems and design ramifications
d. Review of Project Scope
e. Review Task List and determine who will perform each task
f. Identify Missing Tasks and who will do them
g. Identify Ergonomic concerns
h. Assignments
i. Path Forward
Ergonomics Concepts
The following ergonomics concepts shall be reviewed with the team.
a. The goal of ergonomics is to design jobs that can be performed in a safe, efficient, and pain-free manner.
b. The fundamentals belief of ergonomics is that mental and physical capabilities of people are finite and cannot easily be changed. Aspects of work that can be changed are tools, tasks, information, and facilities. Ergonomics emphasizes changing things rather than changing people.
c. Ergonomics examines the task in relation to the person’s capabilities. If task requirements exceed capabilities, then problems are likely to arise. Some problems may be safety and health
related, expressed as an increase in the incidence of cumulative trauma disorders (CTD’s) or other back and muscle problems. Some problems may be performance related, expressed as an increase in error rate or poor quality. Others may be a combination of the two.
d. Consideration of ergonomic principles is a necessary part of the design process to achieve quality design. Ergonomics is not an independent field. Rather, it is embodied in the correct
application of all engineering design disciplines (mechanical, architectural, process control, etc.)
e. Projects should incorporate an ergonomic screening review in the front-end loading (FEL) process. The results of this review should be documented in the Production Design Basis (PDB) and
recommendations should be implemented in the production design process.
f. Ergonomics application must also consider economics. A quality design from the ergonomics standpoint means analysis has been done on all appropriate human/design interfaces and that ergonomics principles have been incorporated into the design. It does not mean all manual tasks have been eliminated, automated, or mechanized.
Ergonomics Concerns
The ergonomics concerns for this project shall be identified by thinking of each task with regard to each of the six human systems. The table below presents each system, the questions each system presents, and the practical aspects of design.
Task Ergonomics Analysis
The team shall identify all of the tasks that will be required of operations and maintenance personnel. Then an analysis of each task shall performed. This analysis shall include:
a. Identification of the personnel who will be expected to perform the task.
b. Determination of whether the task is new, modified, or existing.
c. Identification of any ergonomic concerns by discussion of the tasks in relationship to the six ergonomic systems and the project ergonomic principles.
d. Development of action items requiring further attention.
The following worksheet shall be used to present the record of the task ergonomics analysis.
Table III – Chemical Interaction Matrix
