Construction Site Risk Assessment: A Worked Example

Why is a construction site risk assessment divided into stages?

In a factory, a risk assessment can remain valid for several years because it covers the same machines and the same processes. On a construction site, however, the workplace itself changes every month: what was an excavation pit last month is a basement retaining wall this month and a slab with formwork next month. A construction site risk assessment written as a single table at the start of the project therefore no longer describes the site within a few weeks.

The Regulation on OHS Risk Assessment requires the assessment to be renewed at least every 2, 4 or 6 years depending on the hazard class; but the same regulation requires the assessment to be renewed in full or in part regardless of the period in situations such as a change in technology, equipment or production method, an occupational accident, occupational disease or near miss, and a new hazard arising from outside (Art. 12). On a construction site, these situations occur at almost every stage transition.

In this article, we build a stage-based building work risk assessment for a sample housing site. For the general steps of an assessment, see our article on how to carry out a risk assessment.

Sample project and assessment team

Sample project: A reinforced concrete residential building in Bursa with two basement floors and six standard floors. The main contractor carries out the structural works with its own team; excavation, the tower crane, facade scaffolding, electrical and mechanical installations and tiling are subcontracted. A maximum of 45 workers is planned to be on site at the same time.

Under the regulation, the assessment team includes the employer or their representative, the OHS specialist, the workplace physician, the employee representative, support staff and workers representing different units who know the hazards. On a construction site, add two people to this: the site manager (the person who knows the work programme) and each subcontractor's person in charge on site. Subcontractors carry out, or have carried out, their own risk assessments for their own work; the main contractor's assessment brings together the points where the different jobs affect each other.

In construction work, a health and safety plan is also prepared, and on a site with more than one contractor the coordinator updates this plan as the work progresses. The risk assessment provides input to this plan; they are not the same document. For details, see our article on the Regulation on OHS in Construction Work.

Hazard list by work stage

The first step is to divide the work programme into stages and list the new hazards that each stage brings. The table below is the housing site risk map for our sample project:

Stage	Main works	Key hazards
1. Site set-up	Fencing, containers, temporary electricity and water, access control	Electric shock from temporary electrics, unauthorised entry, conflict between machinery and pedestrians
2. Excavation and shoring	Excavation, earth haulage, shoring, protecting neighbouring building foundations	Collapse, falling from the excavation edge, being struck by machinery, underground services
3. Foundations and basement	Blinding concrete, waterproofing, foundation and wall formwork, rebar, concrete	Falling onto and impalement on starter bars, formwork collapse, concrete pump
4. Structural works	Floor formwork, rebar fixing, concrete pouring, tower crane	Falling from slab edges and openings, falling loads, formwork collapse
5. Walls, roof and facade	Blockwork, roofing, facade scaffolding, external insulation	Falling from scaffolding and roofs, falling materials, manual handling
6. Finishing works	Plastering, installations, tiling, painting, lift installation	Silica dust from cutting tiles and stone, lift shaft, solvents, electric hand tools
7. Dismantling and handover	Scaffold dismantling, landscaping, cleaning	Falls during dismantling, construction machinery, early entry by occupants

At the start of each stage, do not forget the hazards continuing from the previous stage. While structural works are ongoing, the excavation edges in the basement and the temporary electrics are still there.

Example construction site Fine-Kinney scoring

The legislation does not make any particular method mandatory; Fine-Kinney, the L-type matrix and similar methods are common in practice. It is sufficient to state the method you have chosen in the document. In our example we used construction site Fine-Kinney scoring: Risk = Probability × Frequency × Severity. We explain the meaning of the scales in our article on the Fine-Kinney method.

The scores below are a planning assessment carried out before the stage begins: the "before" column shows what the site would be like without measures in place, and the "after" column shows the residual risk once the planned measures are implemented.

Stage	Hazard	Before (P × F × S)	Planned measure	After
1	Electric shock from temporary electrics	3 × 10 × 40 = 1200	Enclosed panels, 30 mA residual current device, cable routing	0.2 × 10 × 40 = 80
2	Collapse in excavation	3 × 6 × 40 = 720	Designed shoring or battered slopes, no loads at the excavation edge, check at entry	0.5 × 6 × 40 = 120
2	Being struck in the excavator's slewing area	3 × 10 × 40 = 1200	Separating the slewing area with barriers, banksman	0.2 × 10 × 40 = 80
3	Falling onto and impalement on starter bars	3 × 6 × 7 = 126	Rebar caps, orderly stacking	0.5 × 6 × 7 = 21
4	Falling from slab edges and openings	6 × 10 × 40 = 2400	Temporary edge protection, locked opening covers, safety net	0.2 × 10 × 40 = 80
4	Fall of a load carried by the tower crane	3 × 6 × 40 = 720	Sling checks, exclusion zone under loads, signaller	0.5 × 6 × 40 = 120
4	Formwork collapse during concrete pouring	1 × 3 × 40 = 120	Formwork and prop design, check before pouring	0.5 × 3 × 40 = 60
5	Falling from facade scaffolding	3 × 6 × 40 = 720	Tagged scaffolding, full guardrails, periodic inspection every 6 months	0.5 × 6 × 40 = 120
6	Silica dust from cutting tiles and stone	6 × 6 × 15 = 540	Wet cutting, cutting machine with extraction, suitable respiratory protection	1 × 6 × 15 = 90
6	Falling down the lift shaft	3 × 3 × 40 = 360	Locked shaft cover, specific work permit for the installation team	0.2 × 3 × 40 = 24

Three lessons emerge from the table. First, the highest scores on a construction site almost always relate to falls from height and heavy loads; so the first line of measures is physical protection, not instructions. Second, some risks in the "after" column remain in the "significant" class; these continue to be monitored with a responsible person and deadline. Third, a lower score depends on the measure actually staying in place on site: a removed edge guardrail takes an 80-point risk back to 2400 overnight.

For details on these topics, see our articles on collapse prevention in excavations and trenches, floor openings and edge protection, tower crane safety and construction scaffold inspection.

How is the risk assessment updated as stages change?

The most practical way to update is to put stage transition checkpoints into the work programme. Hold a short meeting one week before the new stage begins and follow these steps:

List the new works. Which works, which equipment and which subcontractors will come on site in the next stage?
Update the hazard list. Add new hazards, mark hazards from completed works as "closed" and re-score continuing ones.
Prepare the measures on site. Edge protection, scaffolding, nets and opening covers are installed before the work. Installing a measure on the day the work starts leaves the first day unprotected.
Sign off the changed part. In a partial renewal, only the changed section may be updated; but the method used is stated in the document, the pages are initialled and the last page is signed by the team.
Brief the workers. The risks of the new stage are explained in toolbox talks and, if necessary, through job-specific training.
Align with the plan. If there is a coordinator, the relevant section of the health and safety plan is updated in the same week.

There are also events outside the stages that trigger an update:

Occupational accident, occupational disease or near miss: The job in which the event occurred is reassessed afterwards.
New subcontractor: Every new company entering the site brings its own assessment; the main contractor adds the points where this company's work intersects with other work to its own assessment.
Season and weather: Winter conditions, strong winds and rain directly change crane, scaffolding and excavation risks. For cranes and work at height in wind, see our article on crane operations and work at height in strong winds.
Measurement and health surveillance results: For example, if dust measurement during finishing works comes out close to the limit value, the relevant line is re-scored.

For systematic management of changes, read our article on change management and risk revision.

Common mistakes on construction sites

The most common shortcomings we see on construction sites in Bursa and the surrounding provinces are:

A risk assessment exists only for the main contractor; subcontractors have not been asked for their own assessments.
Scores have remained the same across stages; structural works are finished, but finishing-work dust and the lift shaft are not in the table.
The measures column contains unmeasurable phrases such as "care will be taken" or "necessary measures will be taken".
No separate assessment has been carried out for excavation, the tower crane and scaffolding; they all appear in a single line.
The method is not stated in the document, the pages are not initialled and team signatures are missing.
The measure foreseen in the assessment is not in the work programme; a guardrail is written as "required" but it is not clear who will install it and when.

Check your site's hazard class and the related obligations according to the NACE code of your main activity; activities such as site preparation are in the very hazardous class. You can see your specialist, physician and support staff requirements with the OHS obligation calculator. For the items to check on site from set-up to structural works, you can use our construction site OHS checklist article.

At Bursa Sistemer, on construction projects we set up the risk assessment work together with the work programme, update the assessment with a team meeting at every stage transition and combine it with the subcontractors' assessments.

Frequently Asked Questions

How many times is a risk assessment carried out on a construction site?

The regulation requires renewal at least every 2, 4 or 6 years depending on the hazard class; however, on a construction site, renewal is required regardless of the period when equipment, methods and work change. In practice, a partial update is made at every stage transition.

Is the main contractor bound by the subcontractor's risk assessment?

Each subcontractor carries out, or has carried out, a risk assessment for its own work. The main contractor requests these assessments, adds the points where works intersect to its own assessment and ensures coordination. The main contractor's responsibility is not removed by the subcontractor's document.

Is Fine-Kinney mandatory in a construction risk assessment?

No. The legislation does not make any particular method mandatory. Fine-Kinney is useful on construction sites for distinguishing high-frequency work; whichever method you choose, you must state it in the document.

If there is a health and safety plan, is a separate risk assessment needed?

Yes. The health and safety plan is the document that organises the construction work as a whole; the risk assessment is the assessment each employer carries out for its own workers and provides input to the plan. One does not replace the other.