How we calculate: site safety
Every formula and default figure our site safety calculators use. Each figure can be changed in its calculator to match your product. See how we calculate for the method behind all of them.
Silica dust exposure calculator
Open the silica dust exposure calculator
- Concentration after a dust control = measured concentration × (1 − reduction), only where a sourced reduction figure exists
- Concentration inside a mask C_eff = C ÷ APF (assigned protection factor, HSE HSG53)
- Daily exposure, 8-hour TWA = Σ(C_eff × minutes) ÷ 480 min
- Minutes before the limit on one task = WEL × 480 ÷ C_eff
Reaching the limit is a legal maximum, not a target: COSHH requires exposure to be reduced as far as reasonably practicable.
Use water suppression or on-tool extraction first. A mask is the last line of protection and a tight-fitting mask only gives its APF if the wearer has passed a face-fit test.
If your concentration was measured with water or extraction in use, it already includes that control: choose None so it isn't counted twice.
HSE CIS54 gives cutting a paving slab with a diamond blade as taking about a minute: short cuts still add up over a day.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Workplace exposure limit | 0.1 mg/m³ | Regulation or HSE figure HSE EH40/2005 Workplace exposure limits: respirable crystalline silica, 8-hour TWA (see also HSE CIS54 and HSG53 for RPE) Not yet checked against the source | hse.gov.uk (checked 19 October 2026) brief v2 S1: WEL 0.1 mg/m³ 8-h TWA (HSE EH40 / CIS54). Researcher to confirm the current EH40 table entry and the Northern Ireland (HSENI) equivalent. |
| Table | Clause | Nations | Status |
|---|---|---|---|
| Assigned protection factors (APF) for respiratory protective equipment | HSE HSG53 Respiratory protective equipment at work (assigned protection factors) | UK-wide | 1/2 values entered Not yet checked against the source |
| Dust reduction from water suppression or on-tool extraction (fraction removed) | HSE construction dust guidance (CIS54; COSHH essentials CN sheets) | UK-wide | 0/2 values entered Not yet checked against the source |
Gradient and fall calculator
Open the gradient and fall calculator
- Slope s = rise ÷ run. 1 in n: s = 1 ÷ n. Percentage = s × 100. Degrees = arctan(s). mm per metre = s × 1000
- Drop over a length = length × s
- From a measured drop: s = drop ÷ length
Patio falls come from the slab maker's laying guide, drain gradients from Approved Document H, flat-roof falls from the membrane maker and ramp gradients from Approved Document M: use the linked calculators for those figures.
This calculator has no built-in defaults: every figure comes from you or your product's data.
Hand-arm vibration (HAV) exposure points calculator
Open the hand-arm vibration (hav) exposure points calculator
- Points per tool = 2 × a² × T, with a the vibration magnitude (m/s²) and T the trigger time in hours
- A(8) per tool = a × √(T ÷ 8); daily A(8) = √(sum of each tool's A(8)²)
- Action value in points = 2 × 2.5² × 8 = 100; limit value in points = 2 × 5² × 8 = 400
- Trigger time to reach a points total = points ÷ (2 × a²)
Reaching the action value means action is needed to reduce exposure; below it, still reduce exposure as far as reasonably practicable.
Anti-vibration gloves are not a control measure on their own (HSE): choose lower-vibration tools and methods, and limit trigger time.
HSE's own ready reckoner is the authority: use it to check these figures.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Exposure action value, A | 2.5 m/s² A(8) | Regulation or HSE figure Control of Vibration at Work Regulations 2005, reg. 4: daily exposure action value (100 HSE points) Not yet checked against the source | hse.gov.uk (checked 19 October 2026) brief v2 S2: EAV 2.5 m/s² A(8) = 100 points. Researcher to confirm, and the Northern Ireland regulations (2005 NI) equivalent. |
| Exposure limit value, A | 5 m/s² A(8) | Regulation or HSE figure Control of Vibration at Work Regulations 2005, reg. 4: daily exposure limit value (400 HSE points) Not yet checked against the source | hse.gov.uk (checked 19 October 2026) brief v2 S2: ELV 5 m/s² A(8) = 400 points. Researcher to confirm, and the Northern Ireland equivalent. |
Job labour time and cost estimator
Open the job labour time and cost estimator
- Person-days = quantity ÷ output per person per day
- Days on site for a task = person-days ÷ people on the task; tasks are added up as if done one after another
- Labour cost = person-days × your day rate per person
Output rates vary with the job, access, weather and the people doing it: use figures from your own jobs where you can.
Whole days to book rounds the total up to the next full day.
This calculator has no built-in defaults: every figure comes from you or your product's data.
| Table | Clause | Nations | Status |
|---|---|---|---|
| Output per person-day by task (presets) TODO: Researcher to source (brief v2 S7 states no output rates) | TODO: published estimating guide, per row | UK-wide | 0/6 values entered Not yet checked against the source |
Noise exposure calculator
Open the noise exposure calculator
- LEP,d = 10 × log10( Σ (tᵢ ÷ 8) × 10^(Lᵢ ÷ 10) ), with Lᵢ each task's level in dB(A) and tᵢ its time in hours
- Hours at one level before LEP,d reaches a value on its own = 8 × 10^((value − L) ÷ 10)
- At the ear = LEP,d − the reduction you enter for hearing protection; the limit value is checked at the ear
At or above the lower action value employers must assess the risk and provide information and training; at or above the upper action value hearing protection is required and a noise control programme is needed (HSE).
Hearing protectors give less in real use than the figure on the pack: HSE explains how to allow for this.
Reaching a value is not a target: reduce noise exposure as far as reasonably practicable. HSE's own calculator is the authority.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Lower exposure action value | 80 dB(A) LEP,d | Regulation or HSE figure Control of Noise at Work Regulations 2005, reg. 4: lower exposure action value (daily personal exposure) Not yet checked against the source | hse.gov.uk (checked 19 October 2026) brief v2 S3: 80 dB(A) lower action value. Researcher to confirm, and the Northern Ireland (2006 NI) equivalent. |
| Upper exposure action value | 85 dB(A) LEP,d | Regulation or HSE figure Control of Noise at Work Regulations 2005, reg. 4: upper exposure action value (daily personal exposure) Not yet checked against the source | hse.gov.uk (checked 19 October 2026) brief v2 S3: 85 dB(A) upper action value. Researcher to confirm. |
| Exposure limit value | 87 dB(A) LEP,d | Regulation or HSE figure Control of Noise at Work Regulations 2005, reg. 4: exposure limit value (at the ear, taking account of hearing protection) Not yet checked against the source | hse.gov.uk (checked 19 October 2026) brief v2 S3: 87 dB(A) limit value. Researcher to confirm. |
Scaffold hire estimator
Open the scaffold hire estimator
- Bays per elevation = length ÷ bay length, rounded up
- Lifts per elevation = working height ÷ lift height, rounded up
- Scaffold face area = length × working height, added up over the elevations
- Cost = your quoted weekly price × weeks
Bay length and lift height are planning assumptions: the scaffolder sets the real layout, ties, loading and access.
This describes the job only. It is not a scaffold design.
A scaffold on the pavement or road needs a licence from the council: ask the scaffolder who applies.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Bay length | 2.4 m | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 S4: bay length ~2.4 m (assumption). Researcher to source from NASC TG20 or a scaffolder. |
| Lift height | 2 m | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 S4: lift height 2.0 m (assumption). Researcher to source from NASC TG20 or a scaffolder. |