IMPORTANT FORMULAE IN OHSMS

 

Here are important formulae in Occupational Health and Safety Management Systems (OHSMS) that are frequently used for performance measurement, risk assessment, and incident analysis. These formulas are essential for safety professionals, especially in the context of audits, reports, and certifications such as ISO 45001.

---

🔹 1. Incident Rate / Frequency Rate (IFR)

Measures how often incidents occur over a period of time.

$$\text{Incident Rate} = \left( \frac{\text{Number of Recordable Incidents} \times 1,000,000}{\text{Total Hours Worked}} \right)$$

🔹 Alternative multiplier: use 200,000 (based on 100 employees working 40 hours/week for 50 weeks) for OSHA calculations.

---

🔹 2. Severity Rate

Indicates the seriousness of incidents by accounting for lost days.

$$\text{Severity Rate} = \left( \frac{\text{Number of Lost Workdays} \times 1,000,000}{\text{Total Hours Worked}} \right)$$

---

🔹 3. Lost Time Injury Frequency Rate (LTIFR)

Reflects the number of lost-time injuries per million hours worked.

$$\text{LTIFR} = \left( \frac{\text{Number of Lost Time Injuries} \times 1,000,000}{\text{Total Hours Worked}} \right)$$

---

🔹 4. Total Recordable Incident Rate (TRIR)

Covers all OSHA-recordable incidents (injuries and illnesses).

$$\text{TRIR} = \left( \frac{\text{Total Recordable Incidents} \times 200,000}{\text{Total Hours Worked}} \right)$$

---

🔹 5. Risk Assessment Formula (Qualitative)

Used to determine the level of risk in a task or operation.

$$\text{Risk} = \text{Likelihood} \times \text{Severity}$$

📌 Often scored using a risk matrix (e.g., 1–5 scale for both factors).

---

🔹 6. Accident Frequency Rate (AFR)

Used internationally for general comparisons.

$$\text{AFR} = \left( \frac{\text{Number of Accidents} \times 1,000,000}{\text{Total Hours Worked}} \right)$$

---

🔹 7. Near Miss Frequency Rate (NMFR)

Tracks near misses as a leading indicator.

$$\text{NMFR} = \left( \frac{\text{Number of Near Misses} \times 1,000,000}{\text{Total Hours Worked}} \right)$$

---

🔹 8. Man-Hours Calculation

For calculating total hours worked:

$$\text{Total Man-Hours} = \text{Number of Employees} \times \text{Hours Worked per Day} \times \text{Number of Days}$$

---

🔹 9. Occupational Disease Rate

Used for tracking occupational illnesses:

$$\text{ODR} = \left( \frac{\text{Number of Occupational Diseases} \times 1,000,000}{\text{Total Hours Worked}} \right)$$

---

🔹 10. Availability of PPE

To check the availability or compliance rate of PPE:

$$\text{PPE Compliance Rate} = \left( \frac{\text{No. of Workers Wearing PPE}}{\text{Total No. of Workers}} \right) \times 100$$

---