How to Monitor Heat Stress at Work: A Practical Guide to WBGT and OSHA Compliance

As the Occupational Safety and Health Administration (OSHA) continues enforcement of its National Emphasis Program (NEP) on heat, one expectation is becoming clear:

Employers must be able to accurately monitor heat stress conditions and act on that data.

But what does effective heat stress monitoring actually look like in the field?

This guide explains how to measure heat stress at work, why WBGT is the preferred method, and how to implement a practical, defensible monitoring approach.

Why Monitoring Heat Stress Is Critical

Heat conditions can change rapidly throughout the day. Relying on forecasts or general weather data often leads to incomplete or inaccurate assessments of worker risk.

Common challenges include:

• Job sites with mixed sun and shade exposure
• Heat-retaining surfaces like asphalt or roofing
• Limited airflow in indoor or semi-enclosed spaces
• Microclimates across large facilities or job sites

Without onsite measurement, employers risk making decisions based on conditions that don’t reflect actual worker exposure.

Step 1: Choose the Right Measurement Method

One of the most common questions is:

Should you use heat index or WBGT?

Heat Index

• Combines temperature and humidity
• Useful for general awareness

Wet Bulb Globe Temperature (WBGT)

• Incorporates temperature, humidity, solar radiation, and wind
• Reflects how heat is actually experienced by the body

Why WBGT is preferred

WBGT is widely used by:

• Occupational and industrial health professionals
• The U.S. military
• Athletic organizations

Because it provides a more complete and actionable measure of heat stress, especially in outdoor or high-exertion environments.

Step 2: Measure Conditions Onsite

Effective monitoring requires measuring conditions where work is actually happening.

Avoid relying solely on:

• Airport weather stations
• Weather apps
• Regional forecasts

These sources may be miles away and fail to capture jobsite-specific conditions.

Best practice:

Measure heat stress:

• At worker height
• In direct work areas (sun vs shade, indoors vs outdoors)
• At multiple points across large sites

Step 3: Monitor in Real Time

Heat risk is dynamic. A safe morning can become dangerous by mid-afternoon.

Recommended approach:

• Take frequent readings throughout the day
• Increase monitoring during peak heat hours
• Track trends, not just single readings

Real-time data allows safety managers to adjust before conditions become hazardous.

Step 4: Use Data to Drive Action

Monitoring alone is not enough. The goal is to translate data into decisions.

Based on WBGT thresholds, organizations can:

• Adjust work/rest cycles
• Increase hydration breaks
• Modify work schedules
• Pause work when necessary

Many safety guidelines, including ACGIH and military standards, provide clear frameworks for action based on WBGT levels.

Step 5: Document Conditions and Decisions

With increased OSHA enforcement, documentation is critical.

Employers should maintain records of:

• Environmental conditions
• Monitoring frequency
• Actions taken in response to conditions

This creates a defensible record that demonstrates proactive risk management.

How the Kestrel 5400 Heat Stress Tracker Supports Heat Stress Monitoring

To implement an effective monitoring program, organizations need tools that are accurate, portable, and easy to use in real-world conditions.

The Kestrel 5400 is designed specifically for onsite WBGT measurement, enabling:

• Real-time WBGT readings based on environmental conditions
• Portable, handheld monitoring directly at the job site
• Built-in guidance aligned with recognized heat stress standards
• Immediate visibility into changing conditions throughout the day

By measuring heat stress where workers are actually operating, it supports faster, more informed safety decisions.

Common Questions About Heat Stress Monitoring

How do you measure heat stress at work?

The most effective method is to measure environmental conditions onsite using WBGT, which accounts for temperature, humidity, solar radiation, and wind.

Is WBGT required by OSHA?

OSHA does not mandate a specific method, but expects employers to accurately assess heat risk. WBGT is widely recognized as a best practice.

Can I use a weather app instead of measuring onsite?

Weather apps provide general conditions but may not reflect actual jobsite exposure. Onsite monitoring is more accurate and reliable.

How often should heat stress be monitored?

Monitoring should be ongoing throughout the day, with increased frequency during peak heat conditions.

From Monitoring to Safer Worksites

Effective heat stress management starts with accurate, real-time data.

As OSHA continues to prioritize heat safety, organizations that implement onsite monitoring and data-driven decision-making will be better positioned to:

• Protect workers
• Reduce risk
• Demonstrate compliance

Take the Next Step

Learn more about how to measure heat stress and implement WBGT monitoring in your workplace: https://kestrelinstruments.com/prevent-heat-stress