Roger C. Jensen

Safe distance for machinery actuators: Is after-reach speed a constant?

A common setup for industrial machines is to install a pair of actuator buttons a safe distance from the point of operation. Safety codes specify that minimum distance by assuming a constant hand speed of 1.6 m/s. To examine the adequacy of that value, a simulated power press with a moving ram was set up for measuring actual hand speed for three placements of the buttons. For each placement, a randomized complete block experiment with nine students provided after-reach hand speed data. Results indicated that after-reach hand speed is not a constant because it varies both with placement of the buttons and distance within placement.

Stairway Step Dimensions Replication of a Measurement System Study

This paper reports a replication of a prior measurement system study. The earlier study examined the nosing-to-nosing measurement system for measuring steps in a stairway to determine uniformity. In each study, two individuals measured six flights of stairs on two separate occasions. The difference in the first and second study was the different measurers. Step attributes used to define uniformity are riser height and tread depth. The measurers in each study obtained 744 values of riser height and 672 values of tread depth. The ANOVA for each study indicated that less than 4% of the variance in these attributes was due to the measurers; the remainder of variability was due to physical differences in the steps. ANOVA results of this replication led to essentially the same conclusion as the initial study—that the nosing-to-nosing measurement system is acceptable for measuring step dimensions.

Severity Message from Hazard Alert Symbol on Caution Signs

Standards for the design of signal word panels specify different combinations of colors, signal words, and a hazard alert symbol. The warning sign standards of the American National Standards Institute specify a yellow signal word panel, with the word Caution and a hazard alert symbol, for signs marking people hazards. The same panel, without the symbol, is intended for property hazards. The purpose of this study was to determine if the presence or absence of the symbol effectively conveys the intended severity messages. A sample of 59 college students rated their impressions of a Caution sign with and without the symbol. Subjects rated the plain Caution sign as communicating significantly higher severity levels than property damage, indicating that a yellow Caution sign inaccurately communicates a hazard to property. Subjects rated the sign with the symbol as connoting significantly greater severity than the sign without the symbol.

Formats for Section Safety Messages in Printed Manuals

This study compared four formats for safety messages in printed manuals based on layouts found in a new standard of the American National Standards Institute (ANSI Z535.6, 2006). These four designs are specifically for use as section safety messages. Two used a signal word panel, and two used a safety alert symbol (exclamation in a triangle). The four formats were rated by 55 college students from three different classes using a five-point scale for hazardousness. All four messages were presented on the same page of a test booklet, with order balanced using a Latin Square. Results of a Friedman test indicated significant differences in ratings. The ranked order of the formats based on estimated median was yellow safety alert symbol left of the text (3.37), signal word in black panel above text (3.13), signal word in black panel imbedded in first line of text (2.87), and black hazard alert symbol left of the text (2.13). Post-hoc analyses of ratings using a Bonferroni test indicated the signs fit into three groups: the two highest rated signs, the second and third rated signs, and the lowest rated sign.

Alertness-Support Activities for Control Room Operators in Automated Industrial Plants

A survey of control room operators in a nuclear power plant identified practical activities for maintaining alertness during the early morning hours. Nine on-duty operators rated 16 activities they were allowed to do on shift. Activities most effective for alertness were splashing cool water on the face, drinking coffee, and doing things that used muscles. The least effective activities were passive monitoring and studying for exams. The large range of ratings indicates that activity has a major role in operator alertness during the early morning hours.

Stairway Uniformity Measurement: What Lateral Location Should Be Measured?

An experimental study sought to extend understanding of the nosing-to-nosing method for measuring dimensions of steps in a stairway. A human factors expert retained to assist an attorney in a case of injury or death from a stairway fall needs to decide the lateral location for taking the measurements. This experiment was undertaken to provide experts with a justifiable basis for choosing the location. Using a campus stairway and 16 student subjects, a randomized complete block experiment compared their lateral location while performing four tasks—ascending with or without the handrail, and descending with or without the handrail. Results showed task significantly affected lateral distance. Based on findings from this experiment, and some professional judgment, the authors provide recommended ranges for the lateral locations for measuring step dimensions—30 to 38.5 cm for ascending, and 19 to 28 cm for descending.BACKGROUND: This project addressed an unresolved issue involving measurement methods for determining step uniformity. Leading experts on stairway safety agree that lack of step uniformity within a flight contributes to risk of missteps. A relatively new method for precisely measuring step dimensions is the nosing-to-nosing method. An issue in applying the method is lack of agreement on the lateral location to make the measurements. That location depends on where stairway users ascend and descend relative to the width of the steps. A prior investigator examined people descending to determine the lateral distance between the handrail center and the mid-line of the person’s body. He found the median was 44 cm. AIM: The two objectives of the experiment were to: (1) determine if a different set of stairway users will have the same median lateral distance from the handrail as those described in the prior observational study, and (2) determine if the lateral distance of participants is affected by their direction of travel and use of a handrail. METHODS: The investigators established visible distance markers on one stairway in a campus building and videotaped volunteer students ascending and descending the flight of stairs. Each of the 16 participant ascended with and without using the handrail, and each descended with and without using the handrail. Images were printed and analyzed to determine their lateral distance between the inner edge of the handrail and a point midway between the participant’s knees. Results were analyzed statistically to test hypotheses corresponding to the two objectives. RESULTS: The previous study found a median lateral distance of 44 cm when measured from the center of the handrail. Using comparable data, the median found in this study was 25 cm. Results of this study indicated that lateral distance from the handrail is significantly affected by the direction of travel and by use of the handrail. The greatest lateral distance was for ascending with the handrail. The shortest lateral distance was for descending without the handrail. VALUE: Committees develop and periodically revise standards for stairways leading to fire exits and workplace facilities. The practical value of this project is providing empirical evidence that standard developing committees may consider when convening to update their requirements and guidelines on how to measure step uniformity.

Two-Hand Actuator Placement for Power Press Operation: A Reexamination of After-Reach Speeds

This study reexamined data from an earlier study by the U.S. National Institute for Occupational Safety and Health addressing the after-reach speed of press operators—a speed that is a key part of standards for locating two-hand actuator buttons from the point of operation. The 60 participating press operators performed four reaches in each of two button placements. The investigators reported on the fastest of the four for each operator. They concluded that the 1.6 m/s value is inadequate to protect many of the faster press operators. For this paper, all reach speeds were analyzed and used to identify the percentiles of all after-reaches that were slower than several common percentile.