Stacey Benson

Facial Anthropometric Differences among Gender, Ethnicity, and Age Groups

OBJECTIVES The impact of race/ethnicity upon facial anthropometric data in the US workforce, on the development of personal protective equipment, has not been investigated to any significant degree. The proliferation of minority populations in the US workforce has increased the need to investigate differences in facial dimensions among these workers. The objective of this study was to determine the face shape and size differences among race and age groups from the National Institute for Occupational Safety and Health survey of 3997 US civilian workers. METHODS Survey participants were divided into two gender groups, four racial/ethnic groups, and three age groups. Measurements of height, weight, neck circumference, and 18 facial dimensions were collected using traditional anthropometric techniques. A multivariate analysis of the data was performed using Principal Component Analysis. An exploratory analysis to determine the effect of different demographic factors had on anthropometric features was assessed via a linear model. The 21 anthropometric measurements, body mass index, and the first and second principal component scores were dependent variables, while gender, ethnicity, age, occupation, weight, and height served as independent variables. RESULTS Gender significantly contributes to size for 19 of 24 dependent variables. African-Americans have statistically shorter, wider, and shallower noses than Caucasians. Hispanic workers have 14 facial features that are significantly larger than Caucasians, while their nose protrusion, height, and head length are significantly shorter. The other ethnic group was composed primarily of Asian subjects and has statistically different dimensions from Caucasians for 16 anthropometric values. Nineteen anthropometric values for subjects at least 45 years of age are statistically different from those measured for subjects between 18 and 29 years of age. Workers employed in manufacturing, fire fighting, healthcare, law enforcement, and other occupational groups have facial features that differ significantly than those in construction. CONCLUSIONS Statistically significant differences in facial anthropometric dimensions (P < 0.05) were noted between males and females, all racial/ethnic groups, and the subjects who were at least 45 years old when compared to workers between 18 and 29 years of age. These findings could be important to the design and manufacture of respirators, as well as employers responsible for supplying respiratory protective equipment to their employees.

Digital 3-D headforms with facial features representative of the current US workforce.

Existing headforms are based on anthropometric data collected over 30 years ago. In 2003, the National Institute for Occupational Safety and Health conducted an anthropometric survey of 3997 respirator users, of which 1013 subjects were scanned with a Cyberware 3-D Rapid Digitizer. The objective of this study was to create headforms representative of the current US workforce. Ten facial dimensions relevant to respirator fit were chosen for defining a principal component analysis model, which divides the user population into five face-size categories. Mean facial dimensions were then computed to target the ideal facial dimensions for each size category. Five scans in each category were chosen and averaged to construct a representative headform for each size category. Five digital 3-D headforms were developed: small, medium, large, long/narrow and short/wide. All dimensions are within 3 mm of the computed means for the sample population in each size category. Statement of Relevance: This manuscript describes a new approach to constructing headforms that takes into account the facial form (size and shape) of the US workforce. These headforms could be incorporated into respirator research, certification standards and design in efforts to reduce the risk of injury or illness caused by inhalation hazards.

Head-and-Face Anthropometric Survey of Chinese Workers

Millions of workers in China rely on respirators and other personal protective equipment to reduce the risk of injury and occupational diseases. However, it has been >25 years since the first survey of facial dimensions for Chinese adults was published, and it has never been completely updated. Thus, an anthropometric survey of Chinese civilian workers was conducted in 2006. A total of 3000 subjects (2026 males and 974 females) between the ages of 18 and 66 years old was measured using traditional techniques. Nineteen facial dimensions, height, weight, neck circumference, waist circumference and hip circumference were measured. A stratified sampling plan of three age strata and two gender strata was implemented. Linear regression analysis was used to evaluate the possible effects of gender, age, occupation and body size on facial dimensions. The regression coefficients for gender indicated that for all anthropometric dimensions, males had significantly larger measurements than females. As body mass index increased, dimensions measured increased significantly. Construction workers and miners had significantly smaller measurements than individuals employed in healthcare or manufacturing for a majority of dimensions. Five representative indexes of facial dimension (face length, face width, nose protrusion, bigonial breadth and nasal root breadth) were selected based on correlation and cluster analysis of all dimensions. Through comparison with the facial dimensions of American subjects, this study indicated that Chinese civilian workers have shorter face length, smaller nose protrusion, larger face width and longer lip length.

Effect of Exhaled Moisture on Breathing Resistance of N95 Filtering Facepiece Respirators

This study evaluated the effect of exhaled moisture on the breathing resistance of three classes of filtering facepiece respirators (FFR) following 4 h of continuous wear at a breathing volume of 40 l min(-1), utilizing an automated breathing and metabolic simulator as a human surrogate. After 4 h, inhalation and exhalation resistance increased by 0.43 and 0.23 mm of H(2)O pressure, respectively, and average moisture retention in the respirators was 0.26 ml. Under ambient conditions similar to those of the current study, and at similar breathing volumes, it is unlikely that exhaled moisture will add significantly to the breathing resistance of filtering facepiece respirators (FFR) over 4 h of use.

Thermal Burden of N95 Filtering Facepiece Respirators

Increased thermal perceptions that affect comfort are a leading reason for intolerance to wearing respiratory protective equipment. Despite their popularity and use for decades, relatively little is known about the thermal burden imposed by the use of N95 filtering facepiece respirators (FFR) at normal work rates. Twenty healthy subjects exercised at a low-moderate work rate for 1 and 2 h while wearing four models of N95 FFR (two with an exhalation valve) as core and skin temperatures were monitored wirelessly. N95 FFR use resulted in non-significant minimal increases in core temperature and uncovered facial skin (cheek) temperatures. Facial skin temperature under the FFR was significantly increased over baseline values (P < 0.001). Wearing N95 FFR for up to 2 h at a low-moderate work rate does not impose a significant thermal burden on core temperature and uncovered facial skin temperature but significantly increases the temperature of the facial skin that is covered by the FFR. Perceptions of increased body heat when wearing N95 FFR under the test conditions are likely not due to effects on core temperature but may relate more to warming of the facial skin covered by the respirator and warming of the inspired air.

New Respirator Fit Test Panels Representing the Current Chinese Civilian Workers

Respirator fit test panels provide an objective tool for selecting representative human test subjects based upon their facial characteristics for use in research, product development, testing and certification. Fit test panels were typically based upon anthropometric data such as the 1967-1968 survey of American military personnel. In this study, the objectives were to: (i) evaluate the applicability of the recently developed National Institute for Occupational Safety and Health (NIOSH) respirator fit test panels for Chinese workers and (ii) develop new respirator fit test panels using the Chinese survey data. Overall, 95% of the workers in the Chinese survey fall within the NIOSH bivariate and principal component analysis (PCA) panels, suggesting that these panels would also be appropriate for the Chinese population. However, distribution of the subject across the panels was not uniform; only 6.3% of survey participants fell into five cells of the bivariate panel and only 7.2% were found within three cells of the PCA panel. Therefore, new respirator fit test panels with subject dimensions and distributions specific to Chinese workers may be beneficial for certain applications. Two new respirator fit test panels were developed with the same techniques used to create the NIOSH panels. All measurements were weighted to match age and gender distributions of the Chinese population from the 2005 census. The bivariate approach used face length and face width measurements, and the PCA panel was developed using the first two principal components obtained from a set of 10 facial dimensions. Respirators designed to fit these Chinese worker-specific panels are also likely to accommodate >95% of Chinese workers.

Correlation Between Respirator Fit and Respirator Fit Test Panel Cells by Respirator Size

The National Institute for Occupational Safety and Health (NIOSH), recognizing the difficulties inherent in using old military data to define modern industrial respirator fit test panels, recently completed a study to develop an anthropometric database of the measurements of heads and faces of civilian respirator users. Based on the data collected, NIOSH researchers developed two new panels for fit testing half-facepiece and full-facepiece respirators. One of the new panels (NIOSH bivariate panel) uses face length and face width. The other panel is based on principal component analysis (PCA) to identify the linear combination of facial dimensions that best explains facial variations. The objective of this study was to investigate the correlation between respirator fit and the new NIOSH respirator fit test panel cells for various respirator sizes. This study was carried out on 30 subjects that were selected in part using the new NIOSH bivariate panel. Fit tests were conducted on the test subjects using a PORTACOUNT device and three exercises. Each subject was tested with three replications of four models of P-100 half-facepiece respirators in three sizes. This study found that respirator size significantly influenced fit within a given panel cell. Face size categories also matched the respirator sizing reasonably well, in that the small, medium, and large face size categories achieved the highest geometric mean fit factors in the small, medium, and large respirator sizes, respectively. The same pattern holds for fit test passing rate. Therefore, a correlation was found between respirator fit and the new NIOSH bivariate fit test panel cells for various respirator sizes. Face sizes classified by the PCA panel also followed a similar pattern with respirator fit although not quite as consistently. For the LANL panel, however, both small and medium faces achieved best fit in small size respirators, and large faces achieved best fit in medium respirators. These findings support the selection of the facial dimensions for developing the new NIOSH bivariate respirator fit test panel.

Absence of consequential changes in physiological, thermal and subjective responses from wearing a surgical mask.

Twenty subjects treadmill exercised at 5.6 km/h for 1h with and without wearing a surgical mask while being monitored for heart rate, respiratory rate, oxygen saturation, transcutaneous CO2, SpO2, core and skin temperatures, mask deadspace heat and relative humidity, and skin temperature under the mask. Rating scales were utilized for exertion and heat perceptions. Surgical mask use resulted in increases in heart rate (9.5 beats/min; p<0.001), respiratory rate (1.6 breaths/min; p=0.02), and transcutaneous carbon dioxide (2.17 mmHg; p=0.0006), and decreased temperature of uncovered facial skin (0.40 °C; p=0.03). The 1.76 °C increase in temperature of the skin covered by the mask was associated with a mask deadspace apparent heat index of 52.9 °C. Perceptions of heat were neutral to slightly hot, and for exertion ranged from very, very light to fairly light. Surgical mask use for 1h at a low-moderate work rate is not associated with clinically significant physiological impact or significant subjective perceptions of exertion or heat.

Flat Fold and Cup-Shaped N95 Filtering Facepiece Respirator Face Seal Area and Pressure Determinations: A Stereophotogrammetry Study

Twenty subjects underwent quantitative respirator fit testing with two styles (flat fold, cup-shaped) of N95 filtering facepiece respirators (N95 FFRs). Passing a fit test was followed by stereophotogrammetry to determine the face seal area and computation of seal pressure. There were significantly different seal pressures (p < 0.01) between standard size flat fold and cup-shaped N95 FFRs but no significant differences in face seal area. No significant differences were noted in fit factors, but more individuals passed fit testing wearing flat fold respirators. The ability of flat fold N95 FFRs, at lower seal pressures, to obtain similar fit factors as cup-shaped N95 FFR at higher seal pressures offers the possibility of enhanced facial comfort without a loss of protection. Stereophotogrammetry offers a relatively simple, non-invasive technology to evaluate various properties of N95 FFR fit.

Digital 3-D Headforms Representative of Chinese Workers

UNLABELLED Headforms are useful for designing and testing various types of personal protective equipment used to protect millions of workers from occupational hazards in China. Although the Chinese national standard of head-and-face dimensions for adults was first published in 1981, headforms based on those dimensions were never developed. In 2006, an anthropometric survey of 3000 Chinese civilian workers was conducted. As part of the survey, 350 subjects were scanned with a Cyberware 3D Rapid Digitizer. The manual measurements and 3-D digital scans from this survey were used to develop 3-D digital headforms that represent Chinese workers. OBJECTIVE The objective of this study was to develop headforms that represent todays Chinese workers. METHODS Ten facial dimensions relevant to respirator fit were chosen for defining a principal component analysis model which divides the user population into five face size categories. Mean facial dimensions from manual measurements were then computed to target the ideal facial dimensions for each size category. Five scans were chosen from each face size category to be used in the construction process. Selected scans were then averaged to construct a representative headform for each face size category. RESULTS Five digital 3-D headforms were developed: small, medium, large, long/narrow, and short/wide. These distinct sizes of digital 3-D headforms take into account the linear distance between landmarks as well as the surface contours captured during the 3-D scan. The dimensions of constructed headforms were within approximately 4 mm between the corresponding computed means and manual measurements of anthropometric landmarks for the sample population in each size category. CONCLUSIONS These new headforms represent the facial size and shape distribution of current Chinese workers and may be useful for respirator research and development. The Chinese medium headform has a wider face width, shorter face length, and smaller nose protrusion when compared with the current U.S. standard headforms. Upon validation, it may be useful to incorporate these dimensions into Chinese and international respiratory protective devices standards.