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Preliminary hazard analysis (PHA) worksheet

A preliminary hazard analysis, or PHA, is an early, structured look at what could hurt people in a new line, machine or process, done while the design can still change cheaply. The team describes the system, works through prompts such as energy sources, moving parts, chemicals, height and operating modes, then lists each hazard with its cause and worst credible effect, scores it for severity and likelihood, and picks a control from the top of the hierarchy of controls: eliminate, substitute, engineer, then administrative and PPE. It is a first pass, not a detailed study: it comes before a job hazard analysis or a process FMEA, and it tells you where a closer look is needed. This worksheet has four landscape pages: the system and a prompt list, the hazard table, a scale and matrix of our own with four risk classes, and a worked example of a made-up palletising cell. The Excel version works out the class from the matrix, flags high risks that have no control, and counts hazards by class before and after controls.

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Page 1 of the preliminary hazard analysis worksheetFields for the system, phase and team beside two boxes for what the system does and its boundary, and seven groups of hazard prompts with tick boxes.
System description35 hazard promptsHazard tableSeverity and likelihood scalesRisk matrix with four classesHierarchy of controlsRe-score and summaryWorked example
Filled-in Preliminary hazard analysis (PHA) worksheet: a new palletising cell with 14 hazards
The same sheet filled in with the worked example (page 4 of the PDF, illustrative numbers). Open full size (opens the picture in a new tab)

When to use it

When to use a preliminary hazard analysis

  • Before you buy or build a new line, machine or cell, while a guard, interlock or layout change still costs little.
  • When a process changes in a way that brings in new energy, a new material or a new way of working.
  • To decide where a closer study such as a job hazard analysis or a process FMEA is needed, and where it is not.
  • To give a project or capital review a record of the hazards found and the controls chosen before approval.
  • Not for a task that is already running (use a job hazard analysis) or for a failure mode study of a process (use an FMEA).

How to fill it in

  1. 1

    Describe the system and set its boundary

    Write what it does, what goes in and out, where it sits and what is next to it. Say what is in scope and what is not, and note the phase, such as concept or design.

  2. 2

    Work through the prompts

    Go through the energy, moving parts, materials, height and access, people, operating modes and surroundings prompts. Tick any that could apply. Include maintenance, cleaning, jam clearing and start-up, where many injuries happen.

  3. 3

    List each hazard with its cause and effect

    One row for each hazard: what it is, what makes it happen and the worst credible effect on a person. Keep the effect to what could realistically happen, not the worst imaginable.

  4. 4

    Score severity and likelihood

    Score severity from 1 to 4 and likelihood from A to E using the scales on page 3, with the controls already in the design. The matrix gives the risk class.

  5. 5

    Choose a control from the top down

    Try to eliminate the hazard first, then substitute, then isolate people from it with engineering, then change how people work. Use PPE only on top of the layers above, not instead of them.

  6. 6

    Re-score and decide

    Score again with the control in place. Agree who accepts the risk that is left. Anything still in class I or II goes back for a better control before the next stage.

Risk classes

What each risk class means on this worksheet

Severity runs from 1 (minor) to 4 (catastrophic) and likelihood from A (frequent) to E (improbable). The matrix and wording are an example made for this worksheet; adapt them to your own scale and keep them the same across analyses.

  • I

    Name
    Unacceptable
    What to do
    Do not go ahead. Redesign or add controls until the risk is lower.
    Example from the worked example
    Robot arm reaches into the pallet area, severity 4, likelihood B.
  • II

    Name
    High
    What to do
    Agree and fund a control before the next stage, with senior sign-off to continue.
    Example from the worked example
    Stored air in the pneumatic circuit, severity 3, likelihood C.
  • III

    Name
    Medium
    What to do
    Add controls that are reasonably practicable and review at design freeze and start-up.
    Example from the worked example
    Pinch point at the roller transfer, severity 2, likelihood B.
  • IV

    Name
    Low
    What to do
    Accept, and check at commissioning and in routine inspections.
    Example from the worked example
    Cardboard dust at the infeed, severity 1, likelihood B.

What's on the worksheet

The 35 hazard prompts, in seven groups

Work through them for the system you are analysing and tick any that could apply. Each one that applies becomes a row in the hazard table, with a cause, an effect, a score and a control. The Excel version counts the prompts marked Yes that have no hazard written yet.

Energy sources

Anything that stores or delivers energy a person could meet

  1. 1Electrical: mains, control power, batteries, capacitors, static
  2. 2Stored pressure: compressed air, hydraulics, steam, springs under load
  3. 3Heat or cold: hot surfaces, ovens, cryogenics, hot product
  4. 4Gravity: loads that can fall, tip or roll, and anything lifted overhead
  5. 5Radiation, lasers, strong magnets or ultraviolet light

Moving parts and machinery

What can catch, cut, crush or strike

  1. 6Rotating or reciprocating parts, in-running nips and pinch points
  2. 7Robots, manipulators and automatic guided vehicles that move without warning
  3. 8Cutting, punching or pressing actions, and parts that eject or fly off
  4. 9Conveyors and transfer points where a hand can be drawn in
  5. 10Vehicles and forklifts moving near the system

Materials and chemicals

What the system makes, uses or gives off

  1. 11Flammable, combustible or explosive material, dust or vapour
  2. 12Toxic, corrosive or irritating chemicals, in use or in storage
  3. 13Hot, molten or pressurised product, and what happens if it leaks
  4. 14Waste, spills and cleaning chemicals
  5. 15Biological hazards, allergens or contamination of the product

Height, access and space

Where people have to go to run or maintain it

  1. 16Work at height: platforms, ladders, mezzanines, roofs
  2. 17Confined or enclosed spaces that someone must enter
  3. 18Slippery, uneven or cluttered floors and trip points
  4. 19Poor lighting or restricted view at the point of work
  5. 20Blocked or too few exits from the area

People and ergonomics

How the work is done, not only the machine

  1. 21Heavy, repetitive or awkward lifting, reaching or posture
  2. 22Controls and displays that are hard to reach, read or tell apart
  3. 23Tasks that need two people or a lifting aid and have neither
  4. 24Noise, vibration or heat that builds up over a shift
  5. 25Lone working, night work or fatigue at the point of work

Operating modes and phases

Hazards change when the system is not in normal running

  1. 26Start-up, shutdown and restart after a stop
  2. 27Clearing jams and other tasks done close to moving parts
  3. 28Maintenance, cleaning, changeover and adjustment
  4. 29Commissioning, trials and training of new operators
  5. 30Failure of power, air, water or a safety device, and emergency stop

Surroundings and interfaces

What the system touches

  1. 31Neighbouring equipment, walkways and work areas
  2. 32Fire, explosion and spill effects on the rest of the plant
  3. 33Software, controls and networks: unexpected starts or faults
  4. 34Contractors, visitors and people who do not know the area
  5. 35Environmental release: air, water, waste or noise beyond the site

A filled-in example

Illustrative, not a benchmark

An example: a made-up palletising cell at the end of a packaging line, analysed at the design stage, before purchase.

  • The team found 14 hazards: moving robot, dropped loads, stored air, forklift traffic, pinch points, noise, slips, lifting, live parts, a bypassed light curtain, fire, reach, dust and a blocked exit.
  • Two were class I before any control: the robot reaching into the pallet area and a pallet dropped from the gripper. Four were class II, seven class III and one class IV.
  • The controls chosen were mostly engineering: an interlocked gate that stops the robot safely, a gripper that holds on power loss, an isolation valve with a bleed point, a fixed barrier between forklifts and walkers, and a quieter pump.
  • After re-scoring, nothing is left above class III: eight hazards are class III and six are class IV.

Both class I hazards were closed by design changes made before the cell was bought, which is the point of doing the analysis early. The hazards and scores are invented to show how the worksheet is used.

Common mistakes

  • Doing it after the design is fixed

    A preliminary analysis only pays off while the design can still change. Once the machine is built, the only controls left are procedures and PPE.

  • Scoring the worst imaginable outcome

    If every hazard is catastrophic, the matrix stops sorting anything. Score the worst credible outcome and say how you reached it.

  • Leaving out maintenance and jam clearing

    Normal running is often well guarded. The hazards are in start-up, maintenance, cleaning and clearing jams, so go through every operating mode.

  • Jumping to PPE or a procedure

    A rule or a glove is the weakest control. Ask first whether the hazard can be removed or the person kept away from it.

  • Not re-scoring

    A control has not been shown to work until you score the risk again and someone agrees the risk left is acceptable.

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In LeanSuite safety procedures start from marketplace templates, including risk assessments; anyone reports a hazard as a tag from a QR code, and a serious hazard can become a CAPA project with root cause analysis.

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FAQ

Preliminary hazard analysis (PHA) worksheet: common questions

  1. A preliminary hazard analysis is an early, structured look at the hazards of a new system, done while the design can still change. The team lists hazards, their causes and effects, scores the risk and chooses controls. It comes before detailed studies such as a job hazard analysis.

  2. A PHA is a first pass on a whole new system at the design stage. A job hazard analysis breaks an existing task into steps and finds the hazard in each. A failure mode and effects analysis looks at how each part of a process or design can fail. The PHA often tells you where the other two are needed.

  3. As early as there is a concept to analyse and before the design is frozen or the equipment is bought, and again when the design or the process changes. The earlier a hazard is found, the cheaper the control.

  4. Use one your site has agreed and keep it the same across analyses so scores can be compared. This worksheet gives an example: severity 1 to 4, likelihood A to E, and four risk classes. Change the wording to fit your own standards.

  5. A PHA is one kind of risk assessment, used early in a project. A risk assessment can also be a detailed study of an existing task or machine. Check which method your regulator, your customer or your insurer expects for the case you have.

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