Hazard Identification Techniques: PHA, HAZOP, WHAT-IF, and Checklist-Based Screening

Industry Applications

Chemical processing, oil & gas, pharmaceuticals, power generation, water treatment

Key Standards

OSHA 1910.119, IEC 61882, CCPS Guidelines, NFPA 70E (for electrical hazards)

Typical Scale

HAZOP: 1–3 weeks for medium unit; Checklist: <2 hrs; WHAT-IF: 1–2 days for new SOP

Regulatory Trigger

Mandatory for any covered process handling >10,000 lbs of flammable liquid (OSHA PSM)

⚠️ Why It Matters

1

Incomplete hazard identification

↓

2

Undetected failure mode in control system

↓

3

Unmitigated overpressure event

↓

4

Rupture of pressure vessel

↓

5

Toxic release and onsite fatality

↓

6

Regulatory shutdown and $20M+ liability

📘 Definition

Hazard Identification (HAZID) techniques are formal, repeatable engineering methodologies used to proactively recognize potential sources of harm (e.g., fire, release of energy, toxic exposure) and assess their likelihood and consequences. They serve as the foundational step in Process Hazard Analysis (PHA) frameworks mandated by OSHA 1910.119 and IEC 61511, enabling risk ranking, safeguards selection, and verification of design integrity. These methods range from qualitative screening (Checklist, WHAT-IF) to structured, node-based analysis (HAZOP) and comprehensive integrated assessments (PHA).

🎨 Concept Diagram

AI-generated illustration for visual understanding

💡 Engineering Insight

HAZOP isn’t about finding *all* hazards—it’s about finding the *right* hazards with sufficient confidence to justify safeguard investment. A well-facilitated session with strong operational input often reveals more credible scenarios than exhaustive modeling; conversely, skipping operator participation guarantees blind spots in abnormal operations—especially during startup, shutdown, and upset conditions.

📖 Detailed Explanation

Hazard identification begins with recognizing that every engineered system contains inherent energy, material, or information flows that—under deviation—can become harmful. Techniques like Checklists and WHAT-IF provide rapid, accessible screening, ideal for field teams or early-stage designs, but rely heavily on prior experience and may miss systemic or latent interactions.

HAZOP elevates rigor by applying standardized guide words to each process parameter at defined nodes, forcing systematic deviation generation (e.g., 'NO FLOW' → causes: valve stuck shut, pump failure; consequences: reactor overheat, runaway reaction). Its strength lies in structured creativity—but its weakness is dependence on skilled facilitation and complete P&ID documentation.

Modern PHA integrates HAZOP outputs with quantitative methods (e.g., LOPA, QRA) and digital tools (e.g., dynamic simulation, DCS alarm rationalization, digital twin anomaly detection). Advanced practice now includes 'HAZOP 2.0'—where AI-assisted deviation suggestion augments (not replaces) human judgment, and cyber-physical threats (e.g., malicious PLC code, sensor spoofing) are explicitly added to guide word sets per ISA/IEC 62443 requirements.

🔄 Engineering Workflow

Step 1

Step 1: Define scope, boundaries, and operating intent (P&ID, process description, design basis)

→

Step 2

Step 2: Assemble multidisciplinary team with documented competencies (process engineer, operator, instrument tech, safety specialist)

→

Step 3

Step 3: Select technique(s) aligned with risk context (e.g., HAZOP for continuous processes; WHAT-IF for startups/emergencies)

→

Step 4

Step 4: Execute analysis: identify deviations, causes, consequences, existing safeguards, and residual risk

→

Step 5

Step 5: Assign risk priority, recommend action items (e.g., SIS upgrade, procedure revision), and assign ownership with deadlines

→

Step 6

Step 6: Verify implementation via inspection, test records, and management-of-change (MOC) closure

→

Step 7

Step 7: Revalidate every 5 years or after major modification (per OSHA 1910.119(e)(4))

📋 Decision Guide

Rock/Field Condition	Recommended Design Action
New process with no operational history & SIL-2 safety requirement	Conduct full HAZOP + Layer of Protection Analysis (LOPA); validate safeguards with FMEA
Existing plant undergoing minor modification (<5% P&ID change)	Perform targeted WHAT-IF + Checklist review focused on modified nodes only
Batch pharmaceutical process with high-potency API handling	Apply PHA with additional guide words for containment failure, cross-contamination, and operator error; include human factors specialist

📊 Key Properties & Parameters

Node Granularity

1–5 nodes per unit operation (e.g., reactor, separator, pump)

The level of detail at which a process is divided for analysis — e.g., individual valve, pipe segment, or control loop.

⚡ Engineering Impact:

Too coarse → misses localized failure modes; too fine → analysis fatigue and diminishing returns.

Guide Word Coverage

8–12 guide words per parameter, covering ≥95% of IEC 61882-recommended set

The completeness of standard HAZOP guide words (e.g., NO, MORE, LESS, AS WELL AS, PART OF, REVERSE, OTHER THAN) applied across all process parameters (flow, pressure, temperature, level, composition).

⚡ Engineering Impact:

Incomplete coverage increases probability of missing asymmetric or emergent failure scenarios (e.g., reverse flow during pump trip).

Team Competency Index (TCI)

72–94 (validated via ISRM/CCPS competency rubrics)

A composite metric reflecting team members’ combined operational experience, instrumentation knowledge, and safety systems familiarity, scored 0–100.

⚡ Engineering Impact:

Teams scoring <70 show ≥3× higher rate of false-negative hazard identification in validation audits.

Risk Ranking Threshold (RRT)

Risk Matrix Score ≥ 12 (on 5×5 L×C scale), or ALARP threshold ≤ 10⁻⁴ fatalities/year

The predefined risk score cutoff (e.g., Likelihood × Consequence) above which safeguards must be implemented or verified.

⚡ Engineering Impact:

Setting RRT too high defers critical safeguards; too low triggers unnecessary engineering controls and cost overruns.

📐 Key Formulas

Risk Priority Number (RPN)

RPN = Likelihood × Severity × Detectability

Semi-quantitative scoring used in preliminary hazard ranking (common in Checklist and WHAT-IF)

Variables:

Symbol	Name	Unit	Description
Likelihood	Likelihood	dimensionless	Probability of the failure mode occurring
Severity	Severity	dimensionless	Impact or seriousness of the failure mode's effect
Detectability	Detectability	dimensionless	Probability that the failure mode will be detected before it reaches the customer or causes harm

Typical Ranges:

Low-risk utility system

1–25

High-consequence hydrocarbon processing

120–300

⚠️ RPN ≥ 100 requires immediate action; ≥ 200 mandates engineering control within 30 days

🔧 Open Calculator

HAZOP Session Efficiency Ratio (SER)

SER = (Nodes Analyzed × Valid Deviations Identified) / (Session Hours × Team Size)

Metric assessing analytical productivity and facilitation quality

Variables:

Symbol	Name	Unit	Description
SER	HAZOP Session Efficiency Ratio	dimensionless	Metric assessing analytical productivity and facilitation quality
Nodes Analyzed	Number of Nodes Analyzed	count	Total number of process nodes examined during the HAZOP session
Valid Deviations Identified	Valid Deviations Identified	count	Number of credible, non-redundant deviations identified during the session
Session Hours	Session Duration	hours	Total elapsed time of the HAZOP session in hours
Team Size	HAZOP Team Size	persons	Number of active participants in the HAZOP team

Typical Ranges:

Expert-facilitated session

1.8–3.2 nodes·dev/hour·person

Inexperienced facilitator

0.4–1.1

⚠️ SER < 1.2 triggers facilitator retraining and peer review of output

🔧 Open Calculator

🏭 Engineering Example

ExxonMobil Baton Rouge Refinery – Coker Unit Revamp (2021)

N/A (Process Industry Example)

TCI Score

89

Node Count

47 (per P&ID sheet COK-102A)

Time per Node

22 min (avg., per CCPS benchmark)

Guide Words Applied

11/12 (omitted 'EARLY' due to irrelevance to coking cycle)

Residual Risk Items > RRT

3 (all assigned SIL-2 SIS upgrades)

🏗️ Applications

Design stage safety assurance
Management of Change (MOC) validation
Incident root cause investigation support
Audit readiness for PSM compliance

🔧 Try It: Interactive Calculator

🔧

Hazard Identification & Risk Assessment Calculator

Multi-tab calculator for Hazard Identification & R...

Open →

📋 Real Project Case

Automated Assembly Line Robot Cell Risk Assessment

Tier-1 automotive supplier, Ohio plant upgrade

Challenge: New collaborative robot (cobot) integration without physical guarding

Read full case study →

Pharmaceutical Cleanroom HVAC Failure Risk Mitigation Offshore Wind Turbine Blade Repair Confined Space Entry Food Processing Plant LOTO Program Overhaul Urban Tunnel Construction Vibration & Settlement Risk Model

🎨 Technical Diagrams

📚 References

[1]

Guidelines for Hazard Evaluation Procedures — Center for Chemical Process Safety (CCPS)

[2]

IEC 61882: Hazard and operability studies (HAZOP studies) — Application guide — International Electrotechnical Commission

[3]

OSHA 29 CFR 1910.119 Process Safety Management — Occupational Safety and Health Administration

🔗 Related Knowledge

Dynamic Risk Assessment for Changing Work Conditions Human Factors Integration in Hazard Identification: HFACS & STEP Analysis

Hazard Identification Techniques: PHA, HAZOP, WHAT-IF, and Checklist-Based Screening

⚠️ Why It Matters

📘 Definition

🎨 Concept Diagram

💡 Engineering Insight

📖 Detailed Explanation

🔄 Engineering Workflow

📋 Decision Guide

📊 Key Properties & Parameters

Node Granularity

Guide Word Coverage

Team Competency Index (TCI)

Risk Ranking Threshold (RRT)

📐 Key Formulas

Risk Priority Number (RPN)

HAZOP Session Efficiency Ratio (SER)

🏭 Engineering Example

ExxonMobil Baton Rouge Refinery – Coker Unit Revamp (2021)

🏗️ Applications

🔧 Try It: Interactive Calculator

📋 Real Project Case

Automated Assembly Line Robot Cell Risk Assessment

🎨 Technical Diagrams

📚 References

📐 Prerequisites

➡️ Next Step

🔗 Engineering Applications