ISO 8185 Experience from testing

This article is transferred from the old MEDTEQ website written in 2012. Since that time a significant amount of experience testing humidifiers has been obtained and it is planned to update the material below when time allows.


Design and test of humidifiers are difficult, because the exact temperature and humidity provided to the patient is difficult to know and control. Accurate measurement of temperature high humidity flow of air is problematic, and the difficulties of measuring humidity in any environment are widely documented. It is not surprising that many manufacturers simply rely on open loop control based on parameters back at the chamber, where the humidify is 100%, allowing a degree of certainty. But in that case, the actual humidity output to the patient is heavily influenced by flow rates, length of tubing and room conditions.

Beyond performance, the risks of burns can also be difficult to address without also triggering false alarms under normal conditions. The test methods in ISO 8185 also create some issues affecting accuracy, in particular the tests in Annex EE have a major problem, meaning that most manufacturers ignore the test and simply use an external temperature / humidity gauge to confirm the output despite the difficulty.

This article helps to provide some background and theory for those interested in performing ISO 8185 tests.   

The basics (theory)

The main function of a humidifier is to heat a container of water which vaporises the water, adding it to the flow of gas or air and hence creating a heated humidified output. We normally refer to humidity as "relative humidity", such as 50% RH. However, clinically it is the volume of water per unit volume of air that is significant, which is referred to as absolute humidity and has the units of mg/L. A room with 23°C 50% RH has about 10mg/L of water, as vapour in the air. As outlined in ISO 8185, humidifiers should be able to provide at least 10mg/L in 37°C air for non-invasive applications, and 33mg/L for invasive (bypassed airway) applications. 

The figure of 10mg/L is easy and safe to achieve under a wide range of conditions (it is usually well exceeded by most humidifiers). However to provide 33mg/L the risks increase: it is starting to get close to safe limit of 43°C, saturated air (60mg/L). Although the energy is only half the safe limit, manufacturers usually have to exceed 33mg/L in most common conditions, to ensure the output is still above 33mg/L in extreme conditions, such as low room temperatures, high flow rates, and taking into account the errors in measurement and control. Adding in abnormal conditions such as brief interruptions of flow, changes in in flow rates and fault conditions in the control system, it can be tricky to find the right balance.  

To get some concepts of the relation between heat and humidity, we can use some physical parameters of air and water: the “heat of vaporization” (energy required to evaporate water into air) is about 2.26J/mg. The “specific heat” or energy required to increase the temperature of air is about 1.2J/L/°C. Putting these together, we can predict the energy (power) required for a humidifier to operate at a certain flow rates, input and output temperatures.

For example: at 60L/min (1L/s), heating 25°C dry air to 40°C saturated air:

Absolute humidity:   51.3mg/L    (for 40°C)
Power for vaporization:  2.26J/mg x 51.3 mg/L x 1 L/s =  116W
Power for air heating:  1.2J/L/°C x (40 – 25) x 1L/s  =  18W
Total power:  134W

The calculations show that power required is directly proportional to the flow rate. What is also interesting in the example is that most (86%) of the power will be used in vaporization of water, not heating of the air. A change of 1°C in the inlet gas temperature has less than 1% effect on the power, a negligible effect in most cases, particularly if feedback control is provided.

However, the dryness of the gas inlet air does have a large effect. Normal room air of 23°C and 50% relative humidity already has 10mg/L of moisture. In such a case, the humidifier only needs to add 23mg/L to achieve a target of 33mg/L, significantly reducing the required heater power to achieve that target. If feedback is employed, this might not make much effect in the long term, but at high flow rates or during warm up the power might be at the limits of the system. Thus, tests with dry air is the worst case and important.

All of the above just gives us some idea of the power needed. Unfortunately, the temperature and humidity of the delivered gas to the patient, in other words, the output end of any tubing, can be quite different. An unheated tube will have cooling and condensation along the tube, reducing both the temperature and absolute humidity. For example, measurements at a flow rate of 10L/min, with a chamber output of 40°C and 51mg/L has a delivered gas of only 34°C and 38mg/L at the end of a 150cm tube. 

Where does the water go? In a closed system, it might be expected that the water content leaving the chamber should be the same as what comes out the end of the tube. What happens is that water condenses on the inside of the tube, and thus is not delivered to the patient. When enough water builds up, it collects and runs either back into the chamber or to the patient depending on the angle of the tube. To prevent the patient getting this water, the tubing is usually positioned such that the water drains back into the chamber. Thus, the tube in a sense absorbs water from the flow of humidified air or gas.

If the tube is not heated, the humidity at the output is usually 100%, but the temperature is much lower than that at the chamber output. Also there will be a lot of water in the tubing. The temperature at the end of the tube is difficult to predict, but follows a trend with flow rate: at high flow rates the cooling per unit volume of gas is less (because each litre of air spends less time in the tube), leading to higher temperature and humidity output at the patient. However, as mentioned above, at the highest rates the system may reach the limits of heater power, resulting in a fall in output. Thus, with unheated tubing the absolute humidity output usually follows an inverse bathtub type of curve.   

Tube heating is often applied, mainly to prevent excessive build up of water. In this case, the humidity at the patient side can be less than 100%, and the temperature higher than the chamber outlet. The other benefit of tube heating is that overall less heater power is required: because the amount of fluid absorbed in the tube is less, the humidity at the chamber output can be less.

Some tricks in testing

One of the problems in the standard is that dry gas gets used up quickly. Medical grade air is expensive, making the tests very expensive. One trick to lower the cost is to use nitrogen: this is much cheaper and has been found to provide the same results in tests when compared to medical grade air (technical websites indicate also the same). Even then, a 7000L gas bottle can be used up quickly when running tests at high flow rates: just running a 30 minute stabilization period at 60L/min can use 1800L, let alone the actual test.

Another trick was to use room air for stabilization, followed the real test with the dry gas. This works fairly well in mid winter, when the air is dry, but less so in spring or summer. Even with winter air, there is a noticeable change in humidifier performance when switching over to dry gas as can be expected, requiring again a period of stabilization.

To get around this, the air can be dried using a combination of cooling (passing the air through iced water) and then silica gel. The first stage drops the absolute humidity down to around 5mg/L, and the second stage to 1-3mg/L (at 23°C), and amount which is unlikely to influence the results of most tests. At higher flow rates the drying process can be less effective, but this can be overcome by expanding the system. This dried air is perfect for stabilization, and mixed to ensure the residual amount is <1mg/L even at high flow rates.

JIS T 0601-1:2012 Transition and Deviations to IEC 60601-1:2005

This article is copied from the old MEDTEQ website without review. The material is likely to be out of date but retained for reference

On the 1st of June, 2012, Japan published its own version of IEC 60601-1:2005, under the title JIS T 0601-1:2012. The standard is listed under the category of "MOD" which means it is equivalent but with declared modifications. The modifications are summarized in Appendix JC which at this time appear to be only available formally in Japanese (an Engish version of the standard is not yet published). 

The standard has been given a transition period in the Japanese regulation until May 31, 2017. As with Europe, it is expected that that the actual transition period will be driven by particular standards, and most importantly, the updating of the numerous "essential requirement checklists" which are prepared to assist third parties to certify Class II devices according to the PAL regulation (similar to the system used in US under the FDA). These checklists make explicit references to standards, editions and clauses, so these will have to be updated to make way for the series based on the third edtion. It is also noted that third party certificates allowing sale have a validity of 5 years. The overall result is that it could be many years before the third edition is fully applied in Japan. On the other hand, those manufacturers that have to deal directly with the PMDA (generally, the higher risk or novel, new devices) will likely have to follow the May 31, 2017 date. 

The following table provides a list of deviations according to Appendix JC, as translated by MEDTEQ. Although the list has around 15 items, it turns out that the only significant technical change is the allowance to use JIS approved power cords.

During the translation process, it was noted that Appendix JC does not list all the changes in referenced standards from IEC/ISO to JIS versions. For example, under Table 22, IEC 60601-1 references IEC 60085 for insulation systems, in the JIS version this is replaced by JIS C 4003 (which itself is based on but not identical to IEC 60085). One interpretation is that compliance with JIS T 0601-1:2012 can only be claimed if all the referenced JIS standards are checked for deviations. That would be extremely cumbersome, and unlikely to have any real technical impact. Most likely, the ruling will be that overseas manufacturers will be allowed to use IEC 60601-1:2005 + Appendix JC, so only the items in Appendix JC, as shown below, need to be checked as formal deviations.  


Deviation type

Deviation details

Additional notes



“protection against hazards” is corrected to “protection against harm”

No practical change

4.2, Note 2


“… give rise to hazards … “ corrected to “… give rise to harm “

No practical change

4.2, Note 6


Additional note to say that there are many similar errors with respect to hazard and harm throughout the standard

No practical change



JIS version allows the combination SI and alternate units in Table 1

No practical change



If the power cord is in accordance with JIS C 3306 or JIS C 3301, white colour is also acceptable (for the neutral conductor)

 Allows also JIS power cords



If the power cord is in accordance with JIS C 3306 or JIS C 3301, JIS recognized colours are also acceptable for the (active conductors)

 Allows also JIS power cords

8.4.2 c)


“… up to 2V” is corrected to “more than 2V”.

As already corrected in Amendment 1:2012 to IEC 60601-1:2005



Additional sentence before the test is applied to say that the “electrical switch” shall be closed

Listed as being no technical change. This may be intended to point out that the mains switch on the equipment should be “ON” before the test.


“MOOP use” is added to the title

No technical change (just intended to make it clear only for MOOP)


“MOOP use” is added to the title

No technical change (just intended to make it clear only for MOOP)


Power cord is in accordance with JIS C 3306 or JIS C 3301 is also acceptable for this clause. If the temperature of an external metal part which the cord can touch exceeds 60C, double insulated cords are not allowed.

 Allows also JIS power cords

Table 20


The source of the data in Table 20 is changed to JIS B 9711

No technical change, data in Table 20 remains the same



Delete the reference to “unmarked” for pressure vessels

No technical change.

In amendment 1 to IEC 60601-1, “unmarked” has been clarified to mean “no national certification”.  



According to Annex JC, the additional point is simply an example of mixing Class A, B and C materials together.


It is noted that the actual text replaces IEC 60085 with JIS C 4003. This standard is listed as equivalent to IEC 60085 with modifications, and assumed to be equivalent for practical purposes.

No technical change


Table 26



Add a reference to IEC 60950-1 for the limits (as well as IEC 61010)

No technical change



Equipment complying with JIS standards is also permitted within a system.

If an isolation transformer is used, equipment with basic insulation only is also permitted within the system.  

To avoid conflict with local approvals which may use JIS standards which are not aligned or identical to IEC/ISO standards