Medical Gas

Introduction to Medical Gas Analysis

Medical gases are used for patient care in healthcare facilities, dental suites, and laboratories. Typical gases used are Oxygen, Nitrous Oxide, Nitrogen, Carbon Dioxide and Medical Air. This document provides some practical information about the tests needed to guarantee Medical Gas Quality as described in the CSA International publications:

CAN/CSA-Z305.1-92 Non-Flammable Medical Gas Piping Systems
CAN/CSA-Z305.6-92 Medical Oxygen Concentrator
CAN3-Z180.1-00 Compressed Breathing Air and Systems

Note: Please refer to the printed version of the CSA regulations for reference. This is published here for information only.

Routine analysis includes

Carbon Dioxide (CO2) Contamination:

Normal CO2 levels in outdoor air (350 – 450 ppm) or indoor air (500 – 2,500 ppm) are not considered hazardous. However, compressed air with CO2 levels that are within the “indoor air range” can create problems in Self Contained Breathing Apparatus (SCBA) or Supplied Air Breathing Apparatus (SABA) applications. High CO2 levels in breathing air tanks can produce many of the same symptoms as CO poisoning. In addition, high CO2 levels increase breathing rates, which shorten SCBA usage time. Common filtration systems do not remove excessive Carbon Dioxide. Special filters are needed to reduce CO2 levels. Table 1 of CAN3-Z180.1-00 lists a 500 ppm maximum. One of the most common causes for compressed breathing air quality failures is an excessive CO2 content.

Carbon Monoxide (CO) Contamination:

Carbon monoxide (a colourless, odourless gas) is the most toxic contaminant in compressed air. Headaches, dizziness, unconsciousness or death can occur from exposure to elevated CO levels. It enters the breathing air system through the air intake, or is produced by overheating of piston type compressors. The air intake must be placed away from engine exhaust or other sources of carbon monoxide. High pressure compressors can be equipped with a catalyst which converts CO into much less toxic carbon dioxide. Table 1 of CAN3-Z180.1-00 lists a 5 ppm maximum CO content. If a properly functioning, efficient and contaminant free compressor is in use, CO levels will be less than 1 ppm. Detectable CO levels above 1 ppm are “abnormal” & require further investigation.

Halogenated Hydrocarbons Contamination:

Halogenated Hydrocarbons are used as refrigerants, solvents and cleaners.  The combined amount of halogenated hydrocarbons should not exceed 5 ppm. Commonly found halogenated hydrocarbons include

 

 

  • Trichlorotrifluoroethane (Halon 113)

  • Dichlorodifluoromethane (Halon 12)

  • Chlorodifluoromethane (Halon22)

  • chloroform

  • trichloroethylene

  • trichlorofluoromethane (Halon11)

  • tetrachloroethylene

  • tetrachloromethane

  • 1,1,1-trichloroethane

  • vinyl chloride

  • dichloromethane.

Any detectable Halogenated Hydrocarbons above 1 ppm are “abnormal” & require further investigation.

Methane (CH4) Contamination:

Clean, natural air has a Methane value of about 1-2 ppm.

CAN3-Z180.1-00 standard sets a 10 ppm Methane maximum for breathing air.

Methane Values for compressed air that are greater than about 5 ppm are “abnormal” & require further investigation.

High pressure compressors are usually equipped with odour filters (i.e. activated charcoal filters) that remove many organic vapours. A high Methane value could indicate, for example, charcoal filter saturation & the presence of lubricating oil degradation. Other sources of Methane are natural gas and marsh gas.

Odour Evaluation:

Clean air does not have any noticeable odour. Oils, solvents, sulfur compounds and volatile organic vapours are usually the cause of any unacceptable odour in an air sample. Many air compressors have filters to remove these odours. CAN3-Z180.1-00 Standard require that “no pronounced odour” be present in compressed air. A pronounced odour will result in a failed analysis.

Volatile Non-Methane Hydrocarbons Contamination:

Volatile Non-Methane Hydrocarbons (VNMH) which have been mistakenly called “OIL VAPOUR” consists of light, volatile hydrocarbons containing six or less carbon atoms. Examples are propane, butane, ethane, ethylene, hexane etc.

Air compressors (including “non-lubricated” versions) utilize some type of lubricating fluid. Many compressors contain either mineral or synthetic lubricants. Even with all the filters, compressor malfunction or poor maintenance can cause VNMH to contaminate the compressed breathing air. This can cause unpleasant taste and odours, breathing discomfort, nausea, and possibly pneumonia.

An Infrared Spectrometer can be used to measure the VNMH and identify the individual VNMH. 

CSA-Z180.1-00 standard lists a 5 ppm maximum for VNMH. Detectable levels above 1 ppm are abnormal & require further investigation.

Anaesthetic Agents

Nitrous Oxide

Sulfur Dioxide (SO2) Contamination:

Sulfur dioxide is a highly irritating, non-flammable, colourless, toxic gas. It is intensely irritating to the eyes, throat and respiratory tract. Inhalation of sulfur dioxide in concentrations of 8-12 ppm in air causes throat irritation, coughing, constriction of the chest and tearing of the eyes. The odour of sulfur dioxide provides good warning. The normal person can detect 3-5 ppm by volume in air. Lower concentration creates a taste sensation, even before the odour becomes detectable.  Detectable SO2 levels above 1 ppm are “abnormal” & require further investigation.

Water Vapour Content & Dew Point:

The “Dew Point” is the temperature at which water vapour will start to condense from air. This value depends upon water content & pressure. SCBA air is required to be dry enough to prevent malfunctions (i.e. air flow blockage) due to internal condensation or “icing” of the regulators. Elevated water levels can also cause tank corrosion, bacterial growth, and inhibits catalysts that convert carbon monoxide into carbon dioxide.

Standard CAN3-Z180.1-00 states that compressed breathing air equal to or greater than 2216 psig shall have an atmospheric dew point not exceeding -53°C or a water vapour concentration not exceeding 27 ppm. The pressure dew point should be at least 5°C below the lowest temperature to which the cylinder and piping may be exposed at any season of the year.

The measured Dew Point is the quantity of water vapour found in the air sample at ATMOSPHERIC pressure. To determine the temperature at which water vapour may condense and freeze in the pressure reducing regulator, it is necessary to compare the pressure dew point to the ambient temperature at which the SCBA is used. Conversion tables are included in CAN3-Z180.1-00.

For example: The proposed maximum (atmospheric) dew point of -53°C or 27 ppm of water, corresponds to a pressure dew point in the regulator of -12°C or 2148 ppm of water at a line pressure of 2216 psig. However the CSA standard requires that the (pressure) Dew Point not exceed 5°C below the minimum temperature to which any part of the breathing air system is exposed at any season of the year. Thus a compressed breathing air sample with a (atmospheric) Dew Point of -53°C could not be used at a line pressure of 2216 psig in any areas where the temperatures are less than -7°C.

  The standard also states under no circumstances shall the Dew Point (atmospheric) exceed -53°C for systems at or above 15.3Mpa (2216 psig).

and Oil & particulate matter. Certain gases require nitrogen & oxygen detection.

Oxygen (O2) Level Control:

The Oxygen level in compressed air derived from natural or synthetic air should fall within a narrow percent range. Table 1 of CAN3-Z180.1-00 lists an allowable 20% – 22% range for breathing air. Most compressed, natural air samples will have test values of 21% ± 0.5%. The units used to represent O2 levels in are “% by volume”

An oxygen deficiency can occur in a prepared synthetic air or if the compressor air intake is located in an oxygen deficient area. Under very rare conditions, air purification systems can increase the oxygen content of air.

In addition, AirChekLab can detect the presence of a variety of other chemicals and solvents (including cleaning products that could contaminate tanks or pipeline systems.)

To insure quality, Standard Z305.1-92 requires that Medical gases shall be submitted for purity analysis at least once every 12 months.

Additional analyses shall be required following major overhaul modifications or extensive repairs to the gas pipeline system.