Table of Contents

Introduction

Carbon dioxide (CO2) is everywhere: we exhale it, combustion produces it, breweries and fermentation plants use it, fire-suppression systems flood rooms with it, and enclosed spaces fill with it without a whisper. It is non-flammable and non-toxic in the everyday sense, but at elevated concentrations it is a simple asphyxiant that causes headache, drowsiness, rapid breathing and — in a confined space — rapid loss of consciousness. A CO2 gas detector is the instrument that catches that buildup before it catches the worker.

This guide explains how CO2 affects the body, the exposure limits that set your alarms, where CO2 hazards occur, why NDIR is the standard sensor technology, and how fixed and portable monitors should be deployed. Regulatory framing follows EAC (TR CU 012/2011), ATEX and IECEx for Eurasian Union and Middle Eastern industry.

How CO2 Affects the Body

Outdoor air is about 420 ppm CO2. Indoor offices often sit around 800–1,000 ppm. The effects become meaningful as concentration climbs, as the table below summarises.

CO2 concentration	Typical effect (reference ranges)
~420 ppm	Normal fresh air
1,000 – 2,500 ppm	Stuffy air; mild drowsiness and poor concentration
5,000 ppm (0.5%)	OSHA 8-hour permissible exposure limit
10,000 – 30,000 ppm	Headache, rapid breathing, sweating; STEL range
40,000 ppm (4%)	NIOSH IDLH — immediate danger to life or health

The practical point is that CO2 does not announce itself with an odour, and a worker will notice discomfort only after the level is already unsafe. That is why continuous monitoring — not symptom-based judgement — is required.

Where CO2 Hazards Occur

Confined spaces: fermentation tanks, beer and beverage tanks, silos, wells and sewers where microbial activity produces CO2.
Breweries, wineries and biogas plants, where fermentation releases large volumes of CO2.
CO2 fire-suppression and inerting systems that flood a room or equipment enclosure on discharge.
Welding and shielding-gas bays, and industrial CO2 cylinder storage.
Greenhouses and controlled-atmosphere storage, where CO2 is dosed deliberately.
Underground and poorly ventilated spaces, vehicle tunnels and garages where engine exhaust accumulates.

CO2 is about 1.5 times heavier than air, so it accumulates at floor level and in low points — exactly the mounting logic a detection layout must follow.

Why NDIR Is the Standard CO2 Sensor

Carbon dioxide is detected with a non-dispersive infrared (NDIR) sensor. The instrument shines infrared light through a sample chamber at a wavelength absorbed by CO2 and measures how much light is absorbed. NDIR sensors are stable, specific to CO2, require no consumable fuel cell and measure over a wide range from ambient up to 0–5% or higher. They are the correct technology for both fixed room monitors and portable confined-space instruments.

NDIR sensors do drift slowly and need periodic calibration against a known span gas, but they are far more stable than electrochemical cells for CO2. Keep the inlet clean, protect it from dust and oil mist, and recalibrate at the manufacturer’s recommended interval.

Fixed vs Portable CO2 Monitoring

A permanently occupied fermentation area, CO2 suppression zone or underground space needs fixed monitoring. The HD9300 fixed transmitter mounts low near the likely accumulation point, sends 4–20 mA / RS485 / MBUS to the DCS or plant controller, and switches dual alarms and forced ventilation. With an Ex d IIC T6 Gb enclosure and –40 °C to +70 °C operation it suits cold Russian cellars and hot Gulf enclosures.

See the fixed detector: HD9300 Fixed Gas Detector with LCD Display

See the controller: HD6000 Fixed Gas Alarm Controller (2–128 channels)

Confined-space entry and personal response need portable monitoring. A single-gas portable such as the HD600, fitted with an NDIR CO2 cell, gives the entrant a personal ppm-level alarm. For general multi-gas entry, the HD620 four-in-one covers H2S, CO, O2 and LEL — the standard confined-space set.

See the portable detector: HD600 Single-Gas Portable Gas Detector

See the portable detector: HD620 Four-In-One Pump Portable Gas Detector

For a single room or equipment enclosure, the HD6100 single-point wall-mounted all-in-one controller combines detector, display and local alarm.

Hangwei CO2 Monitoring Solutions

Henan Hangwei Sensing Technology Co., Ltd. has more than 20 years of manufacturing experience, 20 patents and 10 production lines. We supply fixed and portable CO2 detectors, controllers and custom sensor packages for EAC, ATEX and IECEx-oriented projects, with OEM/ODM and global distributor recruitment.

Fixed CO2 monitoring: HD9300, Ex d IIC T6 Gb, –40 to +70 °C, 4–20 mA/RS485/MBUS, dual relays, IR remote calibration.
Portable CO2 monitoring: HD600 single-gas NDIR, or HD620 four-in-one for mixed confined-space entry.
Controllers: HD6000 from 2 to 128 channels; HD6100 single-point all-in-one.
Custom packages: NDIR CO2 ranges, mixed configurations and detector-plus-controller systems.

FAQ

What is the OSHA limit for carbon dioxide?

5,000 ppm as an 8-hour time-weighted average, with a short-term exposure limit around 30,000 ppm. The NIOSH IDLH is 40,000 ppm (4% by volume).

Why is CO2 detection mounted low?

Carbon dioxide is about 1.5 times heavier than air, so it sinks and accumulates at floor level and in pits. Low placement matches the accumulation pattern and the worker’s breathing zone.

Is CO2 flammable?

No. CO2 itself does not burn, which is why it is used in fire suppression. Its hazard is asphyxiation and displacement of oxygen, so it is monitored together with oxygen in confined-space work.

Can a standard four-gas detector measure CO2?

Most four-gas instruments measure H2S, CO, O2 and LEL, not CO2. For CO2 use a dedicated NDIR portable such as the HD600 single-gas, or a fixed NDIR transmitter.

How often should an NDIR CO2 sensor be calibrated?

NDIR sensors are stable but not drift-free. Calibrate with known span gas at the manufacturer’s recommended interval, typically annually, and check the zero in clean air periodically.

Does poor indoor air quality need a CO2 monitor?

Yes. Elevated CO2 (above ~1,000 ppm) correlates directly with stuffiness, fatigue and reduced concentration. A CO2 monitor also controls demand-controlled ventilation in offices and enclosed plant rooms.

Get Expert Guidance

CO2 monitoring — whether for confined-space entry, fire-suppression discharge or indoor air quality — is a life-safety and comfort system. Hangwei Sensors designs and manufactures fixed and portable NDIR CO2 detectors and controllers for beverage, biogas, fire-suppression and general industry across Russia, the Middle East and worldwide. Contact our engineers for detector placement, alarm set-points, EAC/ATEX documentation and OEM or distributor terms.

Email: hw@hangweisensors.com | Phone: +86 371 6667 0886

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