The TWL-1S is used to monitor and assess thermal risk level indoor and outdoor. It has a smart user-friendly interface which allow users to instantly identify the thermal risk level result based on different colors. Users can also do data logging directly by connecting the device to windows PC via the USB cable. Wireless pager for remote alerting system is available for the TWL-1SR model.

Why Choose TWL-1S

High Functionality
TWL-1S is designed for all kinds of worksites including mining and construction sites.
Built based on scientific research and algorithm for heat stress safety management.
Built-In Datalogger
Record and download TWL data directly on your windows computer via USB cable
World Class Standards
Every device is calibrated to ensure accuracy. Third-party calibration certificate is available upon request.
Learn TWL-1S in 1 Minute

Scarlet TWL-1S is designed to measure WBGT and thermal work limit (TWL) heat index. The TWL measures air temperature, humidity, radiant heat and wind speed to come up with instructions for work, rest and hydration plan. We integrate the algorithm of TWL and work-rest schedule based on the latest guideline. The user-friendly interface even showed different colors to ensure users in line with TWL schedule. For example, red means unsafe for work, yellow means buffer zone and green means safe for work.


TWL-1S Heat Stress Monitor

Smart User-Friendly

Meters were supposed to sense the targets and give readings. Scarlet intends to do more. TWL theory determines the threshold for a safe, fair, and dangerous working environment. Colorful LCD backlight tells you the risk level based on the TWL value.
Work-rest schedule and fluid intake are integrated into the display. A countdown timer shows the time remaining before a recommended rest.

Automatic Warning
(TWL-1SR Model)

The working timer starts counting according to TWL value. When it expired, the device will notify the pager carriers remotely. It reminds you to take actions.

433 MHz technology is used to offer better penetration ability and 200 meter coverage in an open area is achieved. Please note that pager is available in TWL-1SR model.

Sensor Protection

Delicate temperature and humidity sensors are well protected by a replaceable polypropylene (PP) filter in a solid shield, exempting the sensors from dust damage and external strike. A silicone pad protects the mechanism of the anemometer from dust.

Use Cases

This is the way to Heat Safety

Health, safety and environmental protection are among the fundamental concerns of Bauer in Abu Dhabi and they are top priorities for Scarlet.

We Value Customer Success

Scarlet TWL-1S Heat Stress Detector was applied in Al Fara’a General Contracting (AFGCO) project in downtown Abu Dhabi.

Safety at Worksites

Specialist Services in Dubai used TWL-1S to ensure health and safety of people, contractors and others stakeholders.

Where does Scarlet TWL-1S Apply

Tower Cranes
Port Terminal
Chemical Plant
Outdoor Event
Construction site


Air TemperatureRange 0…60 °C / Accuracy ±0.6 °C
Globe Bulb IndoorRange 0...80 °C / Accuracy ±1.0 °C (15...40 °C); ±1.5 °C (others)
Globe Bulb OutdoorRange 0...80 °C / Accuracy ±1.5 °C (15...40 °C); ±2.0 °C (others)
Relative HumidityRange 5...95 %rh / Accuracy ±3% (at 25 °C; 10...90 %rh) ±5% (others)
Wind SpeedRange 0.5...10 m/s / Accuracy ±(2% of reading + 0.2) m/s
DimensionsBody 59 x 37 x 316 mm (w x d x h). Wind cup (top view) diameter 182 mm
Operating range electronics-10…60 °C
Accuracy at 23 ±5 °C±1.0 %rh / ±0.2 K
Power supply / consumption4 AAA 3V battery, power supply 6 mA consumption without lighting
Probe protectionPolypropylene plastic cage
Measurement interval2 seconds
Data loggerYes. Min data rate 1 min up to 60 min, 2,000 data.
Connection InterfaceMini USB (UART)
Calibration / adjustmentScarlet calibration kit
Wireless Connection (Optional)433 MHz (TWL-1SR Model)
  • Wet Bulb Globe Temperature (WBGT)
  • Thermal Work Limit (TWL)
  • Globe Temperature
  • Dry Bulb Temperature
  • Relative Humidity
  • Wet Bulb Temperature
  • Wind Speed

The TWL-1S has been tested and validated by Health Authority – Abu Dhabi in the extreme high temperature and high humidity Gulf region as well as the mines in Australia. The TWL algorithm used by TWL-1S device is the latest version attested by the research team in Curtin University, Australia.


Risk assessment for heat-related illness in the worksite is quite essential in high temperature environments. TWL-1S can be applied at outdoor and indoor working environments. For instance, a health and safety officer can place the TWL-1S at the “hot spot” zone in worksite and continuously monitor environmental parameters. With 200 meters transmission distance of wireless signal, the paging system can actively warn safety officers in real time. TWL-1S is able to help managers set work/rest cycle and hydration plans for workers.

The TWL-1S Heat Stress Detector is certified by CE mark following the EN 61326-1:2006 Electrical Equipment for Measurement, Control and Laboratory Use.
TWL-1S Heat Stress Detector has also received a third party certification for its temperature and humidity sensors from SGS, a globally renowned company for inspection, verification, testing and certification.

As TWL is to mimic the effects of the working environment on laborers, it is suggested the TWL-1S unit should be placed on the worksite where the majority of workers are located. For example, if there is no shade provided on the worksite, the TWL-1S should be exposed to sunlight as most workers are.

However, in order to prolong the machine life, you can place TWL-1S under sunlight while measuring. Before pushing the TWL button, please allow TWL-1S at least 10 minutes in the working environment to get balance. After the TWL level shows up, you can put it back to shade.

The TWL is the thermal work limit. It’s an advanced heat stress index and research found it more useful in workplaces.

The TWL predicts the maximum level of work that can be carried out in a given environment, without workers exceeding a safe core body temperature 38.2 °C (100.8 °F) and sweat rate (< 1.2 kg or 2.6 lb per hour). WBGT does not incorporate a direct measure of wind speed and requires estimation of metabolic rates, which can have a margin of error up to 50%. Heat stress indexes such as WBGT and ISO 7933 do not take into account the effects of long hours of hard work, dehydration, or the impact of personal protective clothing and equipment. WBGT and heat index are too conservative and inappropriate for practical in the extreme working environments such as Middle East countries or high-temperature process industry or mines. Scarlet TWL-1S incorporated both WBGT and TWL index features. You can simply switch heat indices for your need.

Our Customers

What Our Clients Say

TWL-1S’s friendly user interface has assisted me a lot in implementing the new occupational heat exposure prevention system in the field. This is one of the key elements to success.

Dr. Sanad Al Sanadi, Occupational Health Team Leader, ADMA-OPCO

Since Commencing the heat stress management program in November 2013, the project has not had a SINGLE CASE of a heat stress related illness despite air temperatures of 45 degrees.

Simon Lewis, Project Manager, Leighton Contractors Australia

Companies in Abu Dhabi should comply with EHSMS heat safety standards by adopting thermal work limit (TWL) for risk assessment of heat working environment.

Eng. Ibrahim Khalid, HSE engineer, Abu Dhabi Municipality HSE Division
Heat Stress Meter-TWL-1S

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