Carbon Dioxide Hazard Characterization:

Carbon dioxide (CO2) is naturally present in the atmosphere at levels of approximately 0.035%
(350ppm).

CO2 is classified as an asphyxiant – a substance that, in sufficient concentrations – will interfere with respiration. It is dangerous when inhaled in high concentrations (greater than 5% by volume, or 50,000 ppm).

The current threshold limit value (ACGIH TLV) or maximum level that is considered safe for healthy adults for an eighthour work day is 0.5% (5,000 ppm).

A person's exhaled breath is approximately 4.5% carbon dioxide by volume.

Short-term exposure to CO2 at levels below 2% (20,000 parts per million or ppm) has not been reported to cause harmful effects.

Higher concentrations can affect respiratory function and
cause excitation followed by depression of the central nervous system.

High concentrations of CO2 can displace oxygen in the air, resulting in lower oxygen concentrations for breathing.

Therefore, effects of oxygen deficiency may be combined with effects of CO2 toxicity.

Volunteers exposed to 3.3% or 5.4% CO2 for 15 minutes experienced increased depth of breathing. At 7.5%, a feeling of an inability to breathe (dyspnea), increased pulse rate, headache, dizziness, sweating, restlessness, disorientation, and visual distortion developed.

Twenty-minute exposures to 6.5 or 7.5% decreased mental performance. Irritability and discomfort were reported with exposure to 6.5% for approximately 70 minutes.

Exposure to 6% for several minutes, or 30% for 20-30 seconds, has affected the heart, as evidenced by
altered electrocardiograms.

CO2 Exposure Limits:

Of the several industrial hygiene standards-setting groups in this country, the most important and/or most quoted are the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health

Administration (OSHA), and the American Conference
of Governmental Industrial Hygienists (ACGIH) but these are recommended standards, not laws.

Standards promulgated by OSHA (called Permissible Exposure Limits or PELs) have the force of law.

The other standards are advisory. However OSHA claims the power to force compliance with NIOSH "Recommended Standards" if it chooses to do so.

(The main advantage of ACGIH Threshold Limit Values (TLVs) is that they are reviewed and updated
annually; neither NIOSH nor OSHA updates its standards with any regular frequency.)

Carbon dioxide is regulated for diverse purposes but not as a toxic substance.

The U.S. EPA CO2 exposure limits: The U.S. EPA recommends a maximum concentration of Carbon dioxide CO2 of 1000 ppm (0.1%) for continuous exposure.

ASHRAE standard 62-1989 recommends an indoor air ventilation standard of 20 cfm per person of outdoor air or a CO2 level which is below 1000ppm.

NIOSH CO2 exposure limits: NIOSH recommends a maximum concentration of carbon dioxide of 10,000 ppm or 1% (for the workplace, for a 10-hr work shift with a ceiling of 3.0% or 30,000 ppm for any 10-minute period). These are the highest threshold limit value (TLV) and permissible exposure limit (PEL) assigned to any material.

OSHA CO2 exposure limits: OSHA recommends a lowest oxygen concentration of 19.5% in the work place for a full work-shift exposure.

As we calculated above, for the indoor workplace oxygen level to reach 19.5% (down from its normal 20.9% oxygen level in outdoor air) by displacement of oxygen by CO2, that is, to reduce the oxygen level by about 6%, the CO2 or carbon dioxide level would have to increase to about 1.4% 14,000 ppm.

In summary, OSHA, NIOSH, and ACGIH occupational exposure standards are 0.5% CO2 (5,000 ppm) averaged over a 40 hour week, 3% (3,000 ppm) average for a short-term (15 minute) exposure, and 4% (40,000 ppm) as the maximum instantaneous limit considered immediately dangerous to life and health.

All three of these exposure limit conditions must be satisfied, always and together.