Fundamentals of Safety in Design

Every structure, product, or system we design will eventually be built, used, maintained, and one day decommissioned. At each of these stages, real people interact with our designs — and the decisions we make on paper directly affect their safety.

History is full of examples where design choices, seemingly rational at the time, led to catastrophic consequences. Understanding these failures is not about assigning blame — it's about recognising that safety must be designed in, not bolted on afterwards.

Human Factors in Design

During the Second World War, hundreds of military aircraft were lost not due to enemy action, but because cockpit controls for different functions were nearly identical in shape and position. Fatigued, stressed young crews operating under extreme pressure would confuse critical switches. The solution wasn't to retrain pilots — it was to redesign the controls. Engineers introduced tactile coding: each control handle was given a unique shape so pilots could identify it by touch alone. This principle — design for the human, not the ideal operator — remains foundational in safety engineering today.

When Design Affects the Environment

Buildings can create unexpected hazards in their surroundings. Curved or concave facades can focus sunlight like a magnifying glass, generating extreme heat at street level — damaging vehicles, scorching shopfronts, and endangering pedestrians. In such cases, the structural and architectural form itself becomes the hazard, often requiring expensive retrofits that were never part of the original design intent.

Infrastructure Failures

Ageing infrastructure presents another dimension of safety in design. Bridges designed decades ago for lighter traffic loads, with structural elements that are difficult to inspect or maintain, can deteriorate silently until catastrophic failure occurs. The lesson is clear: design must consider not just initial performance, but the entire service life — including inspection access, maintainability, and the possibility that loading conditions will change over time.

Designing for Extreme Events

Critical facilities located in hazard-prone areas must be designed to withstand not just the primary event (earthquake, flood, storm) but also the cascading consequences. A power station that survives the initial shock but loses its cooling systems due to flooding of backup generators has not been adequately designed for safety. The failure mode wasn't the event itself — it was the failure to protect the systems needed to maintain safety after the event.

Safety in Design (SiD) is a systematic approach to integrating risk control measures into the design process as early as possible, with the goal of eliminating or minimising health and safety risks throughout the entire lifecycle of a structure, plant, or substance.

There are four critical elements in this definition:

What SiD Is Not

• It is not about filling out a compliance form at the end of the project
• It is not limited to construction-phase hazards like slips, trips, and falls
• It is not a one-off exercise — it must be revisited whenever the design changes
• It is about principles, critical thinking, and professional responsibility

In Australia, Work Health and Safety (WHS) legislation places specific duties on designers of structures, plant, and substances. These duties exist in each state and territory and carry significant penalties for non-compliance.

The Designer's Duty

A person who designs a structure, plant, or substance that will be used (or could reasonably be expected to be used) at a workplace must, so far as is reasonably practicable:

• Design without risks to the health and safety of those who will construct, use, handle, store, or maintain it — and anyone else who could be exposed
• Eliminate or reduce risks SFAIRP during the design phase
• Identify and manage hazards throughout the entire project lifecycle
• Provide adequate information to anyone given the design — including the purpose, any calculations/testing results, and conditions necessary to ensure safety
• Pass on residual hazards that cannot be eliminated to the client and/or constructor

The Client's Duty

• Participate in the hazard identification process
• Consult with the designer on safety matters
• Pass on safety information from designers to other stakeholders (constructors, maintainers)
• Manage risks to health and safety during maintenance, operation, and demolition phases

The Constructor's Duty

• Inform designers of any new hazards identified during construction
• Consult and cooperate with designers and other duty holders
• Critical: If the constructor or client modifies the design, they become a "designer" under the law and assume the designer's duties

Safety in Design follows a structured risk management approach. This is not unique to SiD — it's the same fundamental process used across all engineering risk management, applied specifically to design decisions.

The Four-Step Process

Rating Risk — Interactive Matrix

In the assess step, you weigh how severe the harm could be (consequence) against how likely it is (likelihood). A risk matrix turns that judgement into a consistent rating that tells you how urgently to act.

Understanding "Reasonably Practicable"

The SFAIRP test requires weighing up several factors:

• Likelihood: How probable is the hazard occurring?
• Consequence: How severe could the outcome be?
• Knowledge: What is known (or ought to be known) about the hazard and available controls?
• Availability of controls: Are there known, suitable solutions?
• Cost proportionality: Is the cost of control grossly disproportionate to the risk? (Note: cost can only justify not implementing a control if it is grossly disproportionate — a high bar)

A Practical Example

Consider a monitoring station where an air filter must be changed monthly, positioned 4 metres above ground level. The obvious approach — using a ladder — introduces fall risk on potentially uneven surfaces. A better design solution: a hinged mounting pole or telescopic mechanism that allows the filter to be serviced from ground level. This is a cheap, practical, well-understood solution that eliminates the working-at-height hazard entirely through design.

Who Should Be Involved?

The breadth of consultation depends on the complexity of the project, but typically includes:

1. Client — the person commissioning the work
2. Design team — structural, civil, mechanical, electrical engineers
3. Other disciplines that interact with the asset (fire, hydraulics, geotechnical)
4. Constructors and principal contractors
5. Maintenance and operations personnel
6. End users and operational staff
7. Regulatory authorities where applicable
8. Specialists (e.g., work health and safety professionals, human factors experts)

The more diverse perspectives involved, the more hazards will be identified and resolved. SiD workshops should be formally recorded — documenting who attended, what was discussed, and what decisions were made.

Identifying Design Hazards

The key question is: "What if this happens?" Not every hazard qualifies — only those where the design is involved and can be changed. Common hazard categories include:

For a bridge design, typical SiD questions might include: Can the crane safely access the site? Is there adequate ground bearing capacity for crane pads? What happens if floating debris strikes the piers? Is there a pedestrian pathway, and if not, what if people attempt to walk across? What happens during a power disruption? What if a vehicle strikes a structural column?

Worked Examples — Design Decisions in Practice

The real test of Safety in Design is what changes on the drawings. Each example below shows a foreseeable hazard, the design that leaves it on site for someone else to manage, and the safe-design decision that removes or reduces it at the source. Notice that no risk score is calculated here — that quantified assessment (the 5×5 consequence-likelihood matrix, initial and residual ratings, and the formal transfer of residual risk) belongs to the risk-management discipline and is covered in depth in our HSE Risk Assessment course (CSEE-HSE02). SiD's job is the design decision that comes first.