57 An Introduction to Process Safety

Accident – the occurrence of a sequence of events that produce unintended injury, death or property damage

Safety – strategy of accident prevention

Loss prevention – prevention of injury to people, damage to the environment, loss of equipment, inventory, production, reputation or economic loss

Hazard – a chemical or physical condition that has the potential to cause an accident (example of significant chemical plant hazard: flammable, explosive, reactive & toxic hazards)

Risk – the probability of an accident occurring and the consequence of it

Incident – loss of control of material of energy (e.g. leak in a pipe)

Scenario – a sequence of events causing the hazard to result in an accident

Outcome/Consequence – the physical manifestation of an accident

Safety Triangle

The safety triangle shows three essential aspects to achieve workplace safety:

Each of these aspects highlight different key pieces needed in an organization to ensure it can operate safely. Expanding on each aspect of the safety triangle:

Technical – characterization and control of hazards

Management – policies and procedures for safety

Cultural – motivating people to do things safely

Statistics on incidents

OSHA – Occupational Safety & Health Administration
\begin{align*}
& \text{incident rate} = \text{incidents per 100 worker per year}\\
& \text{ every working year} = 2000 \text{ hours}\\
& \text{incident rate} = \text{incidents per 200,000 hours exposure}
\end{align*}

FAR – Fatal Accident Rate
\begin{align*}
& \text{fatalities per 1000 employee over their working life}\\
& =10^8\text{ hours of exposure} \\
& 50 \text{ years pf exposure} × 2000 \text{ hrs/yr} × 1000 \text{ employees}
\end{align*}

Fatality Rate – per person per year – exposure poorly defined

For these statistics, smaller is better!

Personal vs. Process Safety

process safety – low frequency, potentially higher consequence

personal safety – higher frequency, generally lower consequence

Why do Accidents Occur?

We choose to handle dangerous process materials and energies to make value-added products that can be very beneficial.

• If we handle these materials, there is a potential for accidents
• Things can be done to reduce the likelihood and severity of accidents to negligible or tolerable levels

How do accidents occur?

Major Process Industry Incidents and Their Properties

Here we consider the impact of three general categories of the worst types of process industry incidents fire, explosion, and toxic release.

The Hazard Pyramid

The incidents that do not result in any damage (or near misses) are defined by when the event did not lead to harm but only because of happenstance or luck[latex]^{[1]}[/latex]. It is important for us to report these incidents and learn from them.

Common Types of Process Industry Incidents

One Way to Tackle Hazards

Inherently safer design: permanently and inseparably reduce or eliminate process hazards [latex]\rightarrow[/latex] what we don’t have in the process we don’t need to control

Design Strategies to Enhance Safety

For every risk assessment, ask:

• What can go wrong & how?
• What are the chances (probability)?
• What are the consequences?

If the risk is not acceptable, modify the design and go through the risk assessment process again before proceeding to the next stage of the design process.

Inherently Safer Design Strategies

When should we incorporate safety in the design process?

We can implement changes in designs to improve safety at any point. But as with most design processes, it is generally least expensive to do so at the start of the design process.