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HAND DRYING: STUDIES OF THE HYGIENE AND
EFFICIENCY OF DIFFERENT HAND DRYING METHODS

Keith Redway & Brian Knights

THE APPLIED ECOLOGY RESEARCH GROUP,
SCHOOL OF BIOSCIENCES,
UNIVERSITY OF WESTMINSTER,
115 NEW CAVENDISH STREET,
LONDON  W1W 6UW

(Tel:  +44 (0)20 7911 5000;   Fax: +44 (0)20 7911 5087;

E-mail: redwayk@wmin.ac.uk;     Internet: www.wmin.ac.uk/~redwayk

Sponsored by the Association of Makers of Soft Tissue Papers

October 1998

Studies carried out since 1993 out at the University of Westminster have consistently shown that warm air dryers do not perform as well as paper towels or continuous cotton towels in terms of speed, drying efficiency, hygiene and microbial environmental contamination. This summary highlights the main findings and conclusions of these studies.

Previous studies on hand hygiene have mainly concentrated on the effect of hand washing and the type of soap on the bacterial contamination of the hands. However, it has been shown that the hand drying method is as important as the hand washing method in reducing the number of bacteria on the hands and in minimising the risk of transfer of these organisms to food and other objects in the home and after using public toilets.

The steady increase in the incidence of food poisoning cases in the UK and the 1996 E. coli outbreak have increased interest in all aspects of food hygiene and have helped to demonstrate the importance of hand hygiene in wholesale, retail, catering and domestic situations.

Observations of peoples' hand washing and drying habits under natural conditions have been carried out. The results have shown that disposable paper towels and continuous cotton towels are a much quicker and more efficient means of drying the hands than warm air dryers. People rarely use warm air dryers long enough to ensure more than 55-65% dryness and often complete drying by wiping their hands on clothes, etc.

Microbiological studies have shown that using towels after washing helps remove bacteria from the hands and reduces general bacterial counts by an average of 58% (paper) and 45% (cotton). However, in controlled studies warm air dryers were found to significantly increase general bacterial counts on the hands by an average of 255%, with some types of bacteria showing greater increases (e.g. 438% rise with some skin and gut bacteria).

Bacteria have been isolated from the air flow, outlet nozzle and air inlet of warm air dryers in nine types of location (including hospitals, eating places, railway stations, public houses, colleges, shops and sports clubs). Bacteria were found to be relatively numerous in the air flows and on the inlets of 100% of dryers sampled and on 97% of the surfaces of nozzles. Bacterially contaminated air was found to be emitted whenever a warm air dryer was running, even when not being used for hand drying. Staphylococci and micrococci (probably from skin and hair) were blown out of all of the dryers sampled, with 95% showing evidence of the potential pathogen Staphylococcus aureus. At least 6 species of gut bacteria (Enterobacteriaceae) were isolated from the air flow of 63% of dryers, indicating possible contamination by faecal bacteria. The presence of these bacteria in the air flow of such a high proportion of warm air dryers and the increase in the numbers of these bacteria on the hands of the average user demonstrate the potential for the spread of food poisoning organisms such as salmonellas and E. coli.

Whilst some studies have confirmed the results summarised here, other studies differ in their appraisal of the performance of warm air dryers. However, any differences can usually be explained by the fact that these studies have generally used brand new dryers in artificial laboratory situations and/or unusually long drying times. The studies carried out by the University of Westminster used warm air dryers in real locations and drying times that were realistic.

It is suggested that the use of warm air dryers should be carefully considered on hygiene grounds, especially in sensitive locations such as clinics, hospitals, catering establishments and food preparation areas.


Table 1: The main findings and conclusions of the University of Westminster studies on hand drying methods.

 


#

 

 

 

PAPER TOWEL

COTTON TOWEL

WARM
AIR DRYER

 


CONCLUSIONS

1

Average time people spend drying hands

MEN

12 secs

8 secs

20 secs

On average people spend approximately twice as long drying hands using a warm air dryer as they do using paper or cotton towels.

WOMEN

9 secs

8 secs

25 secs

2

Percentage dryness achieved after average drying time

MEN

96%

94%

55%

In normal usage warm air dryers do not achieve the same dryness of the hands as paper or cotton towels.
See Figure 1

WOMEN

93%

94%

68%

3

Average time to achieve 95% dryness


BOTH
SEXES

12 secs

10 secs

43 secs

Warm air dryers take approximately 4 times as long as towels to achieve the same dryness of the hands. Most people use dryers for considerably less than 43 seconds (see point 1 above).

4

Average time that a warm air dryer remains switched on (dryer cycle time)


N/A

30 secs

Most people do not use the full drying time (see point 1 above) but even if they did, hands will only be about 80% dry. See Figure 1

5

Average temperature of air flow of warm air dryer


N/A

55oC

This temperature is insufficient to kill most bacteria emitted in the air flow of dryers.

6

Percentage of people who dry their hands on clothes, hair, etc. after using drying method


MEN

0%

20%

43%

A high proportion of people finish drying their hands by wiping them on their clothes, hair, etc. after using warm air dryers. This is probably because hands are not usually as dry after using a warm air dryer as after using paper or cotton towels (see point 2 above).


WOMEN

5%

4%

39%

7

Average change in general bacterial numbers on fingertips after drying

 

BOTH
SEXES

-58%

-45%

+255%

Paper and cotton towels help reduce the numbers of bacteria on the hands. Warm air dryers significantly increase the numbers of all types of bacteria, including potentially pathogenic types. This is mainly due to the inadequate drying of the hands and also to bacteria emitted in the air flow.
See Figure 2

8

Average bacterial counts in 25-second air flow and swab counts from the outlet nozzle and air inlet of warm air dryers

AIR FLOW

N/A

153

Paper and cotton towels show negligible levels of bacterial contamination. Most warm air dryers are contaminated with bacteria; some very heavily. Bacteria are blown out of dryers onto the hands of users, into the general environment and can also be found in the outlets and inlets.
See Table 2

OUTLET

N/A

540

INLET

N/A

1980

 


#

 

 

 

PAPER TOWEL

COTTON TOWEL

WARM
AIR DRYER

 


CONCLUSIONS


General conclusions:

The studies have shown that on average warm air dryers do not perform as well as paper or cotton towels with any of the assessments of hand drying efficiency that were tested, i.e.

  • speed  (warm air dryers are slower than towels at drying the hands)

  • drying efficiency  (in normal usage warm air dryers do not dry the hands as well as towels)

  • hand hygiene  (in normal usage the number of bacteria on the hands is
    increased by warm air dryers but reduced by towels)

  • environmental contamination  (bacteria are emitted in the air flow of warm air dryers)


Other studies and reports:

ITEM

MAIN POINTS

COMMENTS

The Pennington Group. Report on the circumstances leading to the 1996 outbreak of infection with E. coli O157 in Central Scotland. (1997). The Stationery Office.

The importance of the provision of hand washing facilities in food premises was emphasised. The transmission of E. coli O157 from person to person via the faecal-oral route was discussed.

No recommendations as to the method of hand washing and drying are given but their importance is certainly assumed.

Patrick, D.R., Findon, G. & Miller, T.E. (1997). Residual moisture determines the level of touch-contact associated bacterial transfer following hand washing. Epidemiology & Infection, 119, No. 3, 319-325.

Damp hands were shown to facilitate the translocation of bacteria to objects. Adequate hand drying reduced the numbers of bacteria translocated. Warm air dryers were shown to take significantly longer than towels to have an effect. A 10-second towel dry followed by a 10-second use of a warm air dryer is suggested as a hand drying procedure.

This study confirms our earlier conclusions that hand drying is as important as washing in reducing the bacterial load on the hands and also the superior performance of towels. However, our results would preclude the use of a warm air dryer. It is possible that these workers used a new dryer before it had become contaminated in use.

Blackmore, M.A. (1989). A comparison of hand drying methods. Catering & Health, 1, 189-198.

Showed that warm air dryers, unlike towels, do not remove bacteria from the hands. Found bacterial contamination of dryers. Some of the bacteria isolated were potential pathogens.

Many of these results are confirmed by the University of Westminster studies.

Meers, P.D. & Leong, K.Y. (1989). Hot-air hand driers. Journal of Hospital Infection, 14, 169-171.

Both of these studies suggested that warm air dryers are a safe means of drying the hands. The second study used a dryer set up in a laboratory safety cabinet with filtered air.

Both studies used unrealistic times for drying the hands (45 seconds and 1 minute respectively). The average time people use dryers is 20-25 seconds.  See Table 1

Laboratory set-ups may give rather different results from real toilets. This is why the University of Westminster studies tested hand drying methods in actual toilets, not just laboratories.

Matthews, J.A. & Newsom, S.W.B. (1987). Hot air electric hand driers compared with paper towels for potential spread of airborne bacteria. Journal of Hospital Infection, 9, 85-88.


Any inquiries about this report should be directed to :

Keith Redway,
School of Biosciences,
University of Westminster,
115 New Cavendish Street,
London   UK
W1W 6UW

Telephone: +44 (0)20 7911 5000
Fax: +44 (0)20 7911 5087 (Please mark any correspondence FAO Keith Redway)
E-mail:
redwayk@westminster.ac.uk


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Photographs of hand drying methods

Details of other research

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These pages designed, written and maintained by Keith Redway
Telephone: +44 (0)20 7911 5000   Ext. 3686
Fax: +44 (0)20 7911 5087 (Please mark any correspondence FAO Keith Redway)
E-mail:
redwayk@westminster.ac.uk

These pages last updated: 10 February 2009


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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Table 2: The identifications of some of the bacteria isolated from the air flow of warm air dryers,
the types of location where they were found and the percentage of dryers contaminated.

IDENTIFICATION (DESCRIPTION)

TYPES OF LOCATION
OF DRYER

% DRYERS CONTAMINATED

Staphylococcus aureus
(potential pathogen commonly found on the skin; can cause boils, abscesses, toxic shock syndrome, food poisoning, etc.)

All types of location (hospitals, clinics, fast food outlets, public houses, universities, colleges, railway stations, department stores, sports clubs, supermarkets)

95%

Other staphylococci and micrococci
(skin bacteria, sometimes pathogenic)

All types of location

91%

Enterobacteriaceae (mainly inhabitants of human gut, indicators of faecal contamination, some types cause food poisoning and other problems):

All types of location

63%

Citrobacter freundii

Fast food outlet

3%

Serratia species

University

3%

Enterobacteria species

University, public house

6%

Proteus/Morganella species

Most types of location

45%

Hafnia alvei

Public house

3%

Yersinia species

Fast food outlet

3%

Bacillus species
(usually environmental contaminants)

Fast food outlets, intercity railway station, department stores

14%

Aeromonas species

Fast food outlet, university

6%

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