PUBLISH UNITED STATES COURT OF APPEALS FOR THE TENTH CIRCUIT

________________ _________________ ESMERALDA CASTANEDA; JOSHUA J. PETERS; ANDREW RUIZ; ANGELICA GUTIER REZ; JOANN S. LOPEZ; MARIANO GALLEGOS; TIM PRAEUNER; DAWN ALLMER; SAMUEL SANCHEZ; ADAN ABDULLAHI; AMI NO N. GALAL; ISTAHIL FARAH JAMA; ABDIRIZAK M. ABDI; MUHYADIN AU; MOHAMED HOROR; HABIBO A. ELMI; HIBO H. MAALIN; FAIUMA JAMA; BATULA AWL; SADI M. ADAN; ABDIRIZAK AHMED; AHMED ALI GELLE; HABIBA ABDI; KU RESHA S. NOOR; MOHAMED ISSE; MOHAMED A. MOHAMED; ABDI ABDIRAHMAN; MOHAMED MOHAMED; MOHAMED BUROW; ISRAD IBRAHIM; ABDI JAMA; ABDIAZIZ OSMAN; IBRAHIM O. HASSAN; NUR A. ABDULLAHI; ABDUL KADIR ALI; NUR B. SHUBE; ABDIAMAR BARE; SUHAN JAMA; HASSAN FARAH; NAJIMA HANDULE; AHMED SIRAD ABDI; ALI ABDI; ABDULLAHI ABDIVAHMAN; SALEBAN AHMED; ABDIMAHAT ALI; MANUEL GALLEGOU; ABDIRAHMAN HASSAN; SADIYO HASSAN; NIMC MOHAMED; ALI AHMED MUSE; NIMO OMAR; ABDUL PATAH; ASHLEY TAYLOR ; SAHRO JAMA; FARDOWSA ALI; IB RAHIM A. IMAN; AHMED KHALIF; IRAQ I. ABADE; MOHAMED F. JAMA; MOHAMUD MOHAMED AHMED; ANAB ABDI; HAJI ALI MOHAMUD; KAMAL Nos. 14-1217 and 14-1221 FILED United States Court of Appeals Tenth Circuit 

### March 31, 2016
Elisabeth A. Shumaker Clerk of Court2 SALAH; FARDOWSA ANSHUR; SAHRA NUR; TAJIR HERSI, Plaintiffs - Appellants / Cross- Appellees,

v. JBS USA, LLC, Defendant - Appellee / Cross- Appellant, and SWIFT BEEF COMPANY; SWIFT & COMPANY, INC.; JBS SWIFT & COMPANY; JBS S.A., Defendants.

________________ _________________ Appeal from the United States District Court for the District of Colorado (D.C. No. 1:08-CV-01833-RPM)

________________ _________________ Robert L. Wiggins,Jr., Wiggins, Childs, Pa ntazis, Fisher & Goldfarb, Birmingham, Alabama (Robert J. Camp, Wiggins, Childs, Pantazis, Fisher & Goldfarb, Birmingham, Alabama, Diane Vaksdal Smith, Burg Simp son Eldredge Hersh & Jardine, P.C., Englewood, Colorado, and Joseph D. Lane , The Cochran Law Fi rm, P.C., Dothan, Alabama, with him on the briefs fo r Plaintiffs-Appellants/Cross-Appellees. W.V. Bernie Siebert, Sherman & Howard, L.L. C., Denver, Colorado (Kelly K. Robinson, Sherman & Howard, L.L.C., Denver, Colora do and Lori M. Phillips, Sherman & Howard, L.L.C., Atlanta, Georgia, w ith him on the briefs), for DefendantAppellee/Cross-Appellant.

________________ _________________ Before KELLY , HARTZ , and GORSUCH , Circuit Judges.

________________ _________________ HARTZ , Circuit Judge.3 ________________ _________________ Plaintiffs are current and former hourly employees in the slaughter and fabrication operations of a beef-processing plant in Gr eeley, Colorado, now owned by JBS USA, LLC (JBS). Employees on the slaughter line kill the cattle and disassemble them into sides of beef; employees on the fabrication line cut the sides into various beef products. Plaintiffs have been paid under the terms of collective-bargaining agreements negotiated between the United Food and Commercial Worker s International Union (the Union) and JBS. (For convenience we will refer to both JBS and its predecessors as JBS.) Plaintiffs filed suit against JBS in Octobe r 2010, claiming that they did not receive compensation required by the Fair Labor Stan dards Act (FLSA). The disputes concern when the work day begins, when it ends, and what, if any, compensation is due when the production lines halt for a 30-minute meal br eak. After a bench tr ial the United States District Court for the District of Colorado found that Plain tiffs had failed to carry their burden of proof and entered judgment in favor of JBS. Exercising jurisdiction under 28 U.S.C. § 1291, we affirm. The court could properly find that compensation for Plaintiffs’ activities complied with the FLSA.
I. BACKGROUND A. Introduction to the Legal Framework The FLSA typically requires an employer to compensate empl oyees for all the time that the employee spends wo rking on the employer’s behalf. See Smith v. Aztec Well Servicing Co. , 462 F.3d 1274, 1285 (10th Cir. 2 006). The FLSA does not define work , see Smith , 462 F.3d at 1285, but the Supreme Court has defined the term in the4 FLSA as “physical or mental exertion (wheth er burdensome or not) controlled or required by the employer and purs ued necessarily and primarily for the benefit of the employer and his business,” Tenn. Coal, Iron & R. Co. v. Muscoda Local N. 123 , 321 U.S. 590, 598 (1944) (emphasis added). One issue that has been the source of ma ny disputes is when the work day begins and ends. A partial solution is provided by § 4(a) of the Portal-to-Portal Act of 1947, under which commute time and walking to and from the employee’s work station is ordinarily noncompensable. It provides that the term work does not include either (1) walking or travel time to and from the employee’s “actual place of performance of the principal activity or activities which [the] employee is employed to perform” or (2) “activities which are preliminar y to or postliminary to sa id principal activity or activities.” 29 U.S.C. § 254(a). The Act le aves open to dispute, however, what is encompassed by the term principal activity . The Supreme Court has explained that “activities performed either before or after the regular work sh ift, on or off the production line, are compensable . . . if those activities ar e an integral and indispensable part of the principal activities for which covered work men are employed and are not specifically excluded by Section 4(a)(1).” Steiner v. Mitchell , 350 U.S. 247, 256 (1956) (time that battery-plant employees exposed to toxi c chemicals spent changing clothes and showering pre- and post-shift was compensable). In other words, “any activity that is integral and indispensable to a principal activity is itself a principal activity.” IBP, Inc. v. Alvarez , 546 U.S. 21, 37 (2005) (interna l quotation marks omitted).5 To avoid some of the remaining points of controversy, Congress has left a few matters to collective bargaining. After a De partment of Labor inte rpretive bulletin said that changing clothes, at least in some circ umstances, could be an integral part of a worker’s principal activity (and ther efore compensable, as confirmed in Steiner , 350 U.S. at 256), Congress enacted 29 U.S.C. § 203( o ). See Sandifer v. U.S. Steel Corp. , 134 S. Ct. 870, 875–76 (2014). Under that stat ute a collective-bargaining agreement can provide that changing clothes and washing at the beginning and end of the work day are not compensable. The parties have dis puted what activities (such as donning (and doffing) protective gear and picking up (and disposing of) e quipment) can be encompassed by this exclusion from compensation. And they have also disputed whether workers must be compensated for their walk time between th e locker rooms (where they don and doff clothing) and the production lines. We will discuss the applicable law in greater detail below. Another ground for ignoring some activities at the beginn ing and end of the work day is the de minimis doctrine, which originated in Anderson v. Mt. Clemens Pottery Co. , 328 U.S. 680, 692 (1946). “When the matte r in issue concerns only a few seconds or minutes of work beyond the scheduled working hours, such trifles may be disregarded. Split-second absurdities are not justified by the actualities of working conditions or by the policy of the [FLSA].” Id . The de minimis doctrine has been codified (and limited, see Sandifer, 134 S. Ct. at 880 n.8) by the Department of Labor, which has promulgated a rule stating that “insubstantial or insign ificant periods of time beyond the scheduled working hours, which cannot as a practical administrative matt er be precisely recorded6 for payroll purposes, may be disregarded,” 29 C.F.R. § 785.47, although “[a]n employer may not arbitrarily fail to count as hour s worked any part, however small, of the employee’s fixed or regular working time or pr actically ascertainable period of time he is regularly required to spend on duties assigned to him.” Id.; see Reich v. Monfort , 144 F.3d 1329, 1333–34 (10th Cir. 1998) (adopti ng three-factor test to determine whether time is de minimis : “(1) the practical administrative di fficulty of recording the additional time; (2) the size of the claim in the aggregate; and (3) wh ether the claimants performed the work on a regular basis”); id. at 1333 (“There is no preci se amount of time that may be denied compensation as de minimis.”). Once the work day starts, all activity is ordinarily compensabl e until the work day ends. Under the continuous-workday rule pr omulgated by the Secretary of Labor: “[T]o the extent that activities enga ged in by an employee occu r after the employee commences to perform the first principal activity on a pa rticular workday and before he ceases the performance of the last princi pal activity on a particular wo rkday, the provisions of [§ 4 of the Portal-to-Portal Act] have no application.” 29 C.F.R. § 790.6(a); see Alvarez , 546 U.S. at 28. That is, an activity (such as wa lking to or from a wo rk station) that occurs between the first and last principal activities of the day is compensable even if that same activity would be excluded from compen sable time under the Portal-to-Portal Act had it occurred before the first or after the last principal activity of the day. See Alvarez , 546 U.S. at 37. One exception to the continuou s-workday rule is at issu e in this litigation. The employer does not need to compensate employ ees for a bona fide meal break, which is7 ordinarily at least 30 minutes. See 29 C.F.R. § 785.19(a). Th e parties have disputed whether certain activities at the beginning and end of the 30-minute meal breaks at the JBS plant are compensable work and even whether the break meets the requirement for a bona fide meal break. Again, we will discuss the applicable law in more detail below.
B. Work at the Plant and Agreement with the Union To prevent contamination of beef product s, government regulations and JBS rules require workers to wear hair nets, beard ne ts, plastic aprons, plastic gloves, plastic sleeves, cotton gloves, frocks, and surgical scrubs. For wo rker safety, they are also required to wear personal protective equipment such as boots, scabba rds, mesh protective equipment, cut-resistant gloves, hard hats, ear plugs, and safety glas ses. At the beginning of each day, employees go to their lockers to retrieve and put on such items and to retrieve their knives, hooks, and steels. (All Plaintiffs have wielded knives in their JBS jobs.) They then pr oceed to the production floor. Pl aintiffs, dependi ng on their job duties, obtain frocks, cotton and cut-resist ant gloves, and scrubs from supply windows and sanitize their boots, hands, knives, ho oks, and mesh gloves. Knife-wielding employees may sharpen their knives in the knife room. When they leave the production line at the end of the shift, employees remove their equipment and sanitary clothing. They return their frocks, co tton and cut-resistant gloves, and scrubs to their designated areas . They wash their pe rsonal protective and sanitary equipment at wash stations a nd then sanitize it in special tanks. Id. They must also sanitize their hands and boots before walk ing to the locker room to store clothing and equipment.8 Employees perform similar tasks at the be ginning and end of their meal break. They remove their equipment and sanitary clot hing, except for their hard hats, hair nets, beard nets, ear plugs, and safety glasses. They walk to a wash station to wash their boots and sanitize their hands and boots. Fabricat ion employees also turn in their cotton gloves. Before returning to the lines, empl oyees must sanitize their boots and hands and put back on what they had removed. Under a timekeeping practice known as gang time (also sometimes referred to as line time or master time) employees are paid from the time the first product arrives on the production line until the last product leav es the line. A supervisor and a union representative track the time. No one records activities employe es perform off the production line at the beginning and end of the shift and during the meal break, so employees are free to socialize and loiter. In 2000, in an e ffort to compensate employees for some of the unmeasured activities, JBS and the Union e ach hired an industrial engineer to calculate the time needed to don and doff safety clothing and equipment at the beginning and end of the shift and at meal time, and, at the end of the shift, walk to the wash area to clean safety clothing and equipment, wait at the wash area , and wash safety equipment. These studies did not account for increased wa lk times caused by waiting, obst ructions, and congestion. JBS and the Union agreed to incorporate the measured times for the tasks, called plug times, into their 2000 agreemen t as compensable time. The agreement did not, however, account for walk time from the wash area to th e locker room at the end of the day or any walk time at the beginning of the day. Th e time devoted to activities compensated by9 plug times are not measured each day for each employee. Rather, the employee is compensated by “plugging in” the precalculated time for the employee (depending on the employee’s specific job)—that is, adding it to the measured amount of work time. The parties later incorporated the 2000 plug times into their collective-bargaining agreement that was effective from 2004 through 2009. In 2007 the Union and JBS again engaged industrial engineers to measure the time it took employees to complete various tasks. This time JBS’s engineer used a pr ocess called Ease Works that measured the various movements it took to complete a task . For instance, when measuring how long it would take to put on a mesh apron the engine er would add together the times it took to reach out, grab the mesh, lift the mesh, etc. To identify the variou s components of each task, the engineer observed videos of em ployees performing the tasks. The Union’s engineer, however, again calculated times by measuring how long it took employees to complete the tasks on the production floor. Du ring their 2007 studies the engineers also measured how long it took for employees to walk from the cen ter of the locker room to the center of the production floor. JBS and the Union reached an agreement in 2010 to continue to compensate employees as provided in the 2000 agreem ent but negotiated additional plug time to account for pre- and post-shift walking between the locker room and the production floor by using for all employees the distance betwee n the center of the locker room and the center of the production floor. Neither party ha s pointed us to the calculations underlying the 2010 plug-time payments and th ey do not appear to be in th e record. As part of this negotiated agreement, JBS agreed to pa y current employees the additional time10 retroactively for the preceding two-year peri od of November 2007 to November 2009. Those no longer employed were not paid retroactive walk time. C. The Litigation Before the 2010 ag reement, on August 27, 2008, Plaintiffs filed the present putative collective action against JBS under th e FLSA. In an FLSA collective action an aggrieved employee can bring a claim agains t an employer on behalf of himself “and other employees similarly situated.” 29 U. S.C. § 216(b). To become a party, an employee must opt in by “giv[ing] his consent in writing.” Id. ; see Hoffmann-La Roche Inc. v. Sperling , 493 U.S. 165, 173 (1989). Plaintiffs’ complaint contende d that they had not been adequately compensated for pre- and post-shift “time sp ent donning and doffing clothing and protective gear, washing [equipment and themselves], and walking to and from their job posts,” Aplt. App. I at 117. They also sought comp ensation for their entire meal br eak on the ground that it was not a bona fide meal break, or at least fo r their time donning, doffing, washing, and walking at the beginning and the end of m eal breaks. They requested damages for uncompensated work going back two or three years before they file d their complaint in 2008. (Undercompensated employees ordinar ily must bring a claim to recover unpaid wages within two years of accrual of the claim. See 29 U.S.C. § 255(a). But if the employer willfully violated th e FLSA, the limitations period is extended to three years. See id. ) The district court granted partial summary judgment to JBS, ruling that Plaintiffs’ claim for pre- and post-shift changing of clothes was nonco mpensable under 29 U.S.C. §11 203( o ) because it was covered by the collective-bargaining agreement. The parties proceeded to a two-phase bench trial on Plaint iffs’ claims that they were not reasonably compensated for (1) pre- and post-shift waiti ng, walking, and transp orting tools; and (2) mealtime walking, transporting, waiting, washing, and donning and doffing. In the first phase of the bench trial the parties agreed to lim it their evidence to liability issues. Based on video evidence of plant operations, the district court found that there were “substantial amounts of time required in walking from the locker rooms to the assigned positions on the lines and waiting becaus e of congestion in their areas before the beginning and ending of the work performed on the lines.” Aplt. Add. at 9–10 (First Order – Doc. 166). The court also found that JBS “has not provided a full 30 minute meal break and the minimal amounts of pl ug times for donning and doffing during the break do not satisfy the obligation impos ed by the statute and the regulation.” Id. at 13. It noted that “[t]he questions relevant to remedy may require a determination of the reasonableness of the plug times based on th e 2007 measurements,” and “[a]n appropriate remedy for the failure to provide a bon[a] fide 30 minute meal break must be determined.” Id. at 13–14. During the second phase of the bench trial, the court considered the parties’ expert testimony and reports on the reasonableness of the plug times paid to employees. Plaintiffs presented the opinions of Dr. Robert G. Radwin to support their position that the plug times did not reasonably compensate them. He relied primarily on videos of plant operations that included two full daily sh ifts. To obtain his time measurements, he used a video-analysis software program to calculate the time that employees actually12 spent on various activities. Comparing his me asurements to the pr e-2010 plug times, Dr. Radwin concluded that JBS owed Plaintiffs from 1.7 to 14.6 minut es per day beyond the plug times for work on different sh ifts on different production lines. JBS countered with the testimony and repo rt of Dr. Paul S. Adams. Dr. Adams relied on the same videos and evidence as Dr. Radwin, but he used a different method to calculate the times. He broke the relevant activities into elements that corresponded to articles—that is, single items of clothing or personal equipment. The element times were then added to develop estimates for the full set of articles wo rn by various workers. He excluded avoidable delays, such as personal phone use or socializing. Ultimately, his walk times were very similar to the walk tim es JBS began paying in 2010. For instance, he concluded that the pre- and post-shift walk time for slaughter employees was 1.46 minutes, compared to the plug time of 1.43 minutes, and that pre- and post-shift walk time for fabrication employees was 3.25 minutes, compared to the 3.21- minute plug time. Some of his remaining measurements were greater than the plug times under the collective-bargaining agreements , and some were less; but over all his times were slightly longer. Dr. Adams also challenged Dr. Radwin’s videos (and, implicitly, Dr. Adams’s own calculations based on that evidence). He noted that “[t]he video[s] . . . were apparently taken for demonstr ative purposes and were not ta ken to facilitate time study”; “[t]he poor camera angles and lines of sight in the supplied videos prevented the proper capture of many beginning and ending poin ts”; “[t]he obtrusive camera crew was obviously noticed by many subjects and thei r behaviors were affected”; and “[m]any13 activity areas were not included in the videos.” Id . at 1883–84 (Report of Dr. Adams at 7–8). One consequence was that there were “insufficient sample sizes for a scientific study.” Id. at 1884. In addition, Dr. Adams expressed numerous criticisms of Dr. Radwin’s use of the videos. He complain ed that Dr. Radwin measured the time employees chose to take to complete an ac tivity rather than the time the employee was actively engaged in the activity; did not fo llow established scientific methodology for time studies; failed to account for differences among workers in what personal protective equipment they wore; failed to account for workers who di d not wait in line; assigned times to employees who did not actually perform the activity assign ed; and used a walktime methodology that “resulted in double count ing and inflated values due to improper geographical weighting of calculated times.” Id . at 1893 (Report of Dr. Adams at 17). After considering the expert testimony and reports, the district court rejected Dr. Radwin’s opinions and concluded that Plai ntiffs had failed to meet their burden of proving that the plug times did not reas onably compensate them for work time not included in the gang time. The district court also rejected Plaintiffs ’ claim that the entire meal period was compensable. It said that it had incorrectly assumed in its first order that a 30-minute meal break was required under the FLSA. On reconsideration, it concluded that the predominant benefit of the meal break was for the employees because the “predominant purpose of the 30 minute break is to provide an opportunity to eat and the company provides cafeteria services for that purpose.” Aplt. Add. at 20 (Final Order – Doc. 231). To the extent that Plainti ffs were entitled to co mpensation for work performed during the meal break, it ruled that they had not shown that the work time14 exceeded the plug time they had been accorded in the collective-bargaining agreement. The court entered judgment in favor of JBS and dismissed the case. Plaintiffs’ briefs are not clear about what specific relief they are seeking on appeal. As best we can understand: (1) they are seeking walk time before and after their production-line shifts to the extent it has not been properly compensated by plug times paid by JBS; and (2) although they are no lo nger contending that the meal break is not a bona fide meal period, they do seek payment for the time during their break engaged in walking, washing, donning, and doffing no t properly compensated by plug times. We reject Plaintiffs’ arguments. We therefore need not address JBS’s alternative grounds for affirmance—that it acted in go od faith (which can excuse noncompliance with the FLSA,

see 29 U.S.C. § 259), and that Plaintiffs failed to present testimony representative of all the various types of employees included as Plaintiffs, see Reich v. S. Md. Hosp ., 43 F.3d 949, 951–52 (4th Cir. 1995). We note, how ever, that those alternative grounds for affirmance were not properly ra ised as a cross-appeal; an answer brief is the proper vehicle to raise arguments that do not seek great er relief than that affo rded by the districtcourt judgment. See Jennings v. Stephens , 135 S. Ct. 793, 798 (2015); United States v. Madrid , 633 F.3d 1222, 1225 (10th Ci r. 2011) (“The office of a cross-appeal is to give the appellee more than it obtaine d by the lower-court judgment.”)
II. ANALYSIS “When a party appeals from a bench trial, we review the district court’s factual findings for clear error and its legal conclusions de novo.” Gallardo v. United States , 752 F.3d 865, 870 (10th Cir. 2014). “If the district court’s account of the evidence is15 plausible in light of the record viewed in its entirety, [we] may not reverse it even though convinced that had [we] been sitting as the trier of fact, [we] would have weighed the evidence differently.” Anderson v. City of Bessemer City, N.C. , 470 U.S. 564, 573–74 (1985). A. Issues Decided Summarily We begin by quickly dispos ing of several of Plainti ffs’ arguments on appeal. First, they complain that the district cour t did not impose the relie f required by its initial decision after the liability stage of the trial. But that decision did not bind the court. It was an interlocutory decision, which the cour t could revise at any time before final judgment. See Rimbert v. Eli Lilly and Co. , 647 F.3d 1247, 1251 (10th Cir. 2011). The court recognized that it had changed its mi nd on some matters. The opinion after the second stage of trial states: “It must be admitted that the result now reached is contrary to the expectations generated by the previous Order. It is, however, the result of careful reflection on the evidence in this case and the court opinions cited above.” Final Order at 10. We review only that second opin ion, not the one superseded by it. Second, Plaintiffs complain that the district court’s fi ndings of fact and conclusions of law do not satisfy Fed. R. Civ. P. 52(a), which governs findings and conclusions. But a court’s findings and conclu sions are satisfactory if they enable the appellate court to conduct a proper review of the decision below. See OCI Wyo., L.P. v. PacifiCorp , 479 F.3d 1199, 1203–04 (10th Cir. 2007). Plaintiffs’ brief fails to explain how the findings or conclusions in this case fall short on a material issue. Indeed, the argument on this point in th eir opening brief is so vague and general that we could16 properly rule that th e issue is waived. See Baca v. Berry , 806 F.3d 1262, 1276 (10th Cir. 2015). In any event, the district court’s findings and conclusions are adequate for our review. Third, Plaintiffs argue that the distri ct court improperly found that JBS could avoid liquidated damages because it acted in g ood faith. But that issue is moot because we affirm the decision that JBS did no t violate the law in the first place. That leaves two issues to resolve: th e adequacy of compensation (1) for walk times before and after the employee is e ngaged on a production line and (2) for meal breaks.
B. Walk Time at Beginning and End of Shift In district court Plaintiffs challenged the adequacy of the plug times paid by JBS for walk time by employees between the lock er rooms and the production floors at both ends of their shifts. The district court reje cted the challenge becau se it refused to credit the findings by Dr. Radwin, Plai ntiffs’ expert on that matter. The court’s rejection was based largely on the opinion of Dr. Adams, the JBS expert. See Final Order at 8 (“On balance, this Court accepts the opinions of Dr . Adams.”). Dr. Adams expressed the view that even using Dr. Radwin’s questionable da ta, the plug times were reasonably close to, and sometimes greater than, the times necessa ry to perform the various activities. The court concluded that Dr. Radwin’s calculations did “not adequately account for all of the variations involved” in the time it takes diffe rent employees to perform the same activity. Id. at 21. It noted that “Dr. Radwin’s calculations are based on very limited information.” Id . And it said: “[Dr. Adams’s] resu lts are markedly different from those17 of Dr. Radwin. These differences reflect the underlying difficulty in attempting to determine the realities of the workplace by those methods.” Id . at 8. In our view, the court’s rejection of Dr. Radwin’s plug times was reasonable; and we note that on appeal Plaintiffs do not contest the rejection. That leaves the argument raised by Pl aintiffs on appeal, which relies on JBS’s adoption of the plug times included in the 20 10 collective-bargaining agreement for walk time from the locker room to the production floors before the workers’ shifts and for walk time from the wash area to the locker room after the shifts. They argue that JBS essentially conceded in that agreement that those plug tim es are necessary to comply with the FLSA. They therefore clai m that under their complaint f iled in 2008 they can recover this unpaid work time beginning in 2006 (or 2 005 if JBS’s violation of its duty to pay was willful, see 29 U.S.C. § 255(a)). Some workers have already been paid part of what Plaintiffs claim because in 2 010 JBS agreed with the Union that the additional plug times would be paid to current empl oyees for work in 2008 and thereafter (but would not be paid to those no longer employed by JBS in 20 10). As a result, Plaintiffs contend that they all are entitled to back pay beginning in 2006 (or 2005), althou gh those working in 2010 would not receive backpay for work after 2007. The district c ourt refused to order payment for those times because Plaintiffs fail ed to produce credible supporting evidence of the walk times. We affirm, but on an alternative ground ra ised by JBS. We hold that walk times from the locker rooms to the production floor s at the beginning of the shift and from the wash stands to the locker rooms at the end of the shift were not co mpensable work before18 plug times were added for th at activity in the 2010 collective-barg aining agreement between the Union and JBS. Our analys is is as follows: First, under § 203( o ), time at the beginning or end of the workda y devoted to changing clothe s is not compensable if so determined under a collective-bargaining ag reement. Second, the Supreme Court has ruled that time spent donning or doffing items that cannot be described as clothing is also noncompensable under § 203( o ) if performed at the same time as the noncompensable changing of clothes and the period “can, on the whole , be fairly characterized as time spent in changing clothes . . . .” Sandifer v. U.S. Steel Corp. , 134 S. Ct. 87 0, 881 (2014) (internal quotation marks omitted). In partic ular, the time would s till be noncompensable even if workers spend a comparatively small part of th e time gathering or disposing of equipment. Third, agreeing with Sandifer v. U.S. Steel Corp ., 678 F.3d 590, 595–98 (7th Cir. 2012), we hold that if time to perform an activity is noncompensable under § 203( o ), then the activity is not a “princ ipal activity” that begins or e nds the workday. Therefore, walk time between the production floor and the locker room, where noncompensable donning or doffing occurs, is noncompensable under the Portal –to Portal Act. Fourth, agreeing with then-Judge Sotomayor’s opinion in Singh v. City of New York , 524 F.3d 361, 367–70 (2d Cir. 2008), we hold that trav el to the place where the employee performs a principal activity of the job, which is or dinarily noncompensable under the Portal-toPortal Act, does not become compensable ju st because during that travel the employee must carry an item necessary for performance of the work if carrying the item adds negligible time or inconvenience to the tr avel. Therefore, walk time between the production floor and the locker room is noncompensable even if an employee must carry19 equipment on the way. Fifth and fi nally, because the purpose of § 203( o ) is to leave compensability of certain activ ities to collective bargaining, see Sandifer , 134 S. Ct. at 876, it follows that if collective bargaining results in providing some compensation for unmeasured work time, such compensation does not conver t any additional otherwisenoncompensable activities into work time. Therefore, walk time after donning and before doffing that would otherwise be noncompensable does not become compensable just because the collective-bargai ning agreement provides pl ug time for some donning or doffing. We proceed to explain more fully. We begin with 29 U.S.C. § 203( o ). Under that statute, “the compensability of time spent changing clothes or washing is a subject appropr iately committed to collective bargaining.” Sandifer v. U.S. Steel Corp. , 134 S. Ct. 870, 876 (2014). The statute renders those activities noncompensable if they are “excluded from measured working time during the week in volved by the express terms of or by custom or practice under a bona fide collective-bargaining agreement.” 29 U.S.C. § 203( o ) 1 ; see Salazar v. Butterball, LLC , 644 F.3d 1130, 1135 (10th Cir. 2011). Moreover, a collective-bargaining agreem ent can also render noncompensable the donning and doffing of items that are not cl othing as long as that donning and doffing adds relatively little time to the overall donning or doffing process. This was the holding

1 Section 203( o ) states in full: “Hour s Worked.--In determining for the purposes of sections 206 [Minimum wage] and 207 [Max imum hours] of this title the hours for which an employee is employed, there sha ll be excluded any time spent in changing clothes or washing at th e beginning or end of each workday which was excluded from measured working time during the week involved by the express terms of or by custom or practice under a bona fide collect ive-bargaining agreem ent applicable to the particular employee.”20 of Sandifer v. U.S. Steel Corp., 134 S. Ct. 870, 880–81 (2014). The Court did not reach its conclusion by applying the de minimis doctrine. It expressed doubt about the de
minimis doctrine in the § 203( o) context, stating that it “doe s not fit comfortably within the statute at issue here, which, it can fairly be said, is all about trifles—the relatively insignificant periods of time in which employ ees wash up and put on various items of clothing needed for their jobs.” But the an alysis is rather sim ilar to that under the doctrine. Sandifer concerned employees who sought backpay for their time spent donning and doffing 12 items of protective ge ar, which they argued were not clothing subject to § 203( o ). The district court held that the ite ms were all clothes but that even if three items (hardhats, glasses, and earp lugs) were not, the time spent on them was de
minimis

. See id. at 874. The Supreme Court affirm ed that conclusion, but under somewhat different reasoning. It agreed that the employees’ time spent donning and doffing nine of the items qualified as changing clothes under § 203( o ). See id. at 879. And even though the remaining three items were not clothes under § 203( o ), the Court reasoned that on the whole the time could be characterized as changing clothes under § 203( o ). See id. at 881 (“The question for courts is whether the period at issue can, on the whole , be fairly characterized as time spent in changing clothes or washing.” (internal quotation marks omitted)). “If an employee de votes the vast majori ty of the time in question to putting on and off eq uipment or other non-clothes items . . . the entire period would not qualify as time spent in changing clothes under § 203( o ), even if some clothes items were donned an d doffed as well.” Id. “But if the vast majo rity of the time is spent21 in donning and doffing clothes . . . , the en tire period qualifies, and the time spent putting on and off other items need not be subtracted.” Id. It is unclear to us wh en the results under the de minimis doctrine and the on-thewhole test would differ. Perhaps the distin ction is that compensation is required for activities that take only a short period of time if that period is nevertheless comparable to the time it takes to change clothes; in ot her words, the test is whether the time is relatively short, rather than whether it is short on some absolute scale. Sandifer seems applicable here. JBS and the Union have negotiated over the years whether compensation (through plug times) sh ould be provided for activities before the worker arrives at the production line or after the worker departs the production line. Two of those activities are donning and doffing cl othing and equipment in the locker room. We agree with Plaintiffs that not everyt hing they don and doff can be described as clothing. But as we understand the district court’s findings at the end of the trial, the additional time for donning and do ffing such nonclothing items is de minimis . Plaintiffs do not challenge that finding and any challe nge would be unsucce ssful in any event because the finding is a reasonable view (p erhaps the only reasonable view) of the evidence. We conclude that the collective-bargaining agr eement could therefore exclude the locker-room activities fro m compensation under § 203( o ) because under Sandifer , 134 S. Ct. at 881, the locke r-room time was devoted “on the whole” to changing clothes. One could nevertheless argue, however, that even though pickin g up (or returning) equipment and donning (or doffing) noncloth ing items in the locker room are not compensable, those activities are still “principal activities” that start (and end) the22 workday, so the walk times between the locker room and the production floor are compensable. (Recall that unde r the Portal-to-Portal Act, tr avel time is not compensated only if it precedes the first principal activity of the day or follows th e last such activity.
See 29 U.S.C. § 254(a).) We reject the argumen t. Facing the same issue, the Seventh Circuit explained in Sandifer : If [clothes-changing time] is not work time—the workers aren’t being paid and their union has agreed to their not being paid—how can it be one of the ‘principal activities which the employee is employed to perform’? He is required to wear work clothes, and for that matter he is required to show up for work. But he is not employed to show up or employed to change clothes. Not all requirements imposed on employees constitute employment. An employee may be required to call in when he is sick, but unless he is on paid sick leave he is not paid for the time it takes to place the call. 678 F.3d at 596 (internal ellipsis omitted). The court recognized that the Supreme Court had held in Alvarez , 546 U.S. at 37, that absent a co llective-bargaining agreement on the matter, donning and doffing of work clothes at the workplace could be principal activities and walking between the locker room (whe re the donning and doffing occur) and the work station is not exempted from compensability by the Portal-to-Portal Act. But, said the court: Section 203( o ) permits the parties to a colle ctive bargaining agreement to reclassify changing time as nonworking time, and they did so, agreeing that the workday would not start when the workers changed their clothes; it would start when they arrived at their wo rk site. If clothes-changing time is lawfully not compensated, we can’t se e how it could be thought a principal employment activity, and so [the Portal -to-Portal Act] exempts the travel time in this case.23 Sandifer , 678 F.3d at 596–97. The Ei ghth Circuit was persuaded, see Adair v. ConAGRA Foods, 728 F.3d 849, 852– 53 (8th Cir. 2013), and so are we. But see Franklin v. Kellogg , 619 F.3d 604, 619 (6th Cir. 2010 ). After all, in enacting § 203( o ), Congress was trying to eliminate the di sruptions that the [Supreme] Court’s interpretation of the Fair Labor Standa rds Act had caused, and to allow the determination of what is compensable work in borderline cases (is changing into work clothes ‘work’? is walking from a locker room to a work station ‘work’?) to be settled by negotiati on between labor and management. Sandifer , 678 F.3d at 597–98; see also id . at 598 (quoting preamble to the Portalto-Portal Act in support). What about the fact that Plaintiffs carried their tools of the trade (knives or hooks) between the locker room and th e production floors? The trav el from the locker room to the production floor (and back) is excluded from FLSA coverage by the Portal-to-Portal Act unless it follows (or precedes) a principa l activity; and we have just held that Plaintiffs’ locker-room activities are excl uded from being principal activities by § 203( o ) and the parties’ collective-bargaining agreemen t. We do not believe that Plaintiffs’ carrying knives or hooks conv erts what would otherwise be noncompensable walk time into compensable walk time. The decision clos est in point is the Second Circuit opinion
in Singh , written by then-Judge Sotoma yor. The plaintiffs in Singh , city fire-alarm inspectors, argued that they were entitled to compensation for all or part of their time spent commuting to and from work because th eir employer required that they “carry and keep safe necessary inspection doc uments during their commutes.” Singh , 524 F.3d at 364. The Second Circuit rejected their argument. Relying on the Supreme Court’s holding that whether time is work time depends on wh ether the “time is spent24 predominantly for the employer’s benefit or for the employee’s,” Armour & Co. v. Wantok , 323 U.S. 126, 133 (1944), the court held that the predominant benefit of the commute was for the employees, not the employer: “Carrying a briefcase during a commute presents only a minimal burden on th e inspectors, permitting them freely to use their commuting time as they ot herwise would have without the briefcase. . . . While the city certainly benefits from the plaintiffs’ carrying these material s, it cannot be said that the City is the predominant beneficiary of this time.” Singh , 524 F.3d at 368–69. The court concluded that “the mere carrying of inspection documents does not transform plaintiffs’ otherwise non-compensable commute into compensable time.” Id. at 369. It added that its analysis “in many ways resembles a de minimis test.” Id. It cited the Sixth Circuit opinion in Aiken v. City of Memphis , 190 F.3d 753, 759 (6th Cir. 1999), which held that police officers need not be compensated for th eir commuting time even though they must monitor thei r police radios during this travel , “because ‘the amount of work involved in monitoring a po lice radio during a commute is simply de minimis.’” Singh , 524 F.3d at 369 (quoting Aiken , 190 F.3d at 759). Then-J udge Sotomayor concluded, “The point is that, under either approach, wh en an employee is minimally restricted by an employer during a commute, such that his or her use of commuting time is materially unaltered, the commuting time will generally not be compensable under the FLSA.” Id. In the case before us, there is no reas on to believe that carrying equipment increased the walk time to any extent or me aningfully restricted what workers did on their way to the production floor. In fact, the district court noted that “employees are not required to move directly from their lockers to the line ... [or] to their lockers after25 leaving the wash area at the end of the shift. ” First Order at 10–11. (Stopping to wash the equipment on the way to the production floor would delay the trip but Plaintiffs are not challenging on appeal any failure to comp ensate for the wash time, which apparently is represented in the plug times.) Under the Singh analysis, the walk time in this case would not be compensable just because th e worker is carryi ng a knife or hook. There is one more possible wrinkle in this case. If the co llective-bargaining agreement had totally eliminat ed compensation to employees for any of the walk time or clothes-changing time, the ab ove analysis would compel the conclusion that the employees are not owed any additional compensation under th e FLSA. But the agreement did provide plug times to co mpensate for clothes-changing time. We therefore may not be able to apply literally the ho lding in the Seventh Circuit opinion in Sandifer that noncompensable work activity cannot be “principal activity” that marks the beginning or end of the workday. See 678 F.3d at 596–97. 2 Nevertheless, the proposition on which the reasoning in Sandifer was founded is that § 203( o ) was enacted to leave to collective bargaini ng whether certain ac tivities at the beginning and end of the workday off the production line should be comp ensated. It would make no sense to leave to collective bargaining whether there should be compensati on for such activities but not

2 Section 203( o ) excludes from employment hours th e time “excluded from measured working time” by the collec tive-bargaining agreement. We assume, without deciding, that plug times are “measured wo rking time” that has been adopted, not excluded, by the collective-bargaining ag reement, even though they are not measured during the work day (the plug time added to the worker’s time is based on one-time calculations incorporated in the collective-bargaining agr eement). If plug times are not considered “measured working time,” howe ver, then the activity covered by plug times is “excluded from meas ured working time,” and th is case is identical to Sandifer in this respect.26 how such activities are to be co mpensated. What possible po licy rationale would require the negotiating parties to be limited to an a ll-or-nothing regime—either providing for no compensation for the activities or fully compensating all of them? We therefore give § 203( o ) the commonsense reading that it leaves to collective bargaini ng the extent to which employees will be compensated for activities that could be rendered totally noncompensable through that provision. Applying this analysis to Plaintiffs’ clai ms, we conclude that (1) all the walk time for which they seek back pay could have been rendered noncompensable by the collective-bargaining ag reement (through § 203( o )), and (2) therefore they were entitled only to compensation for walk time provided through the plug times in the collectivebargaining agreements in effect during the time at issue. We affirm the district court’s denial of the walk-time claims because Plai ntiffs are seeking great er compensation than provided in the collectiv e-bargaining agreements. C. Meal Break Plaintiffs’ final issue requires less discu ssion. They claim that they have been inadequately compensated for time spent donning, doffing, cl eaning, and walking during their 30-minute meal break. Unde r 29 C.F.R. § 785.19(a), bona fide meal periods are not considered work time and are no t compensable. A bona fide meal period is “[o]rdinarily 30 minutes,” but “[a] shorter period may be long enough under sp ecial conditions.” Id. For a break to qualify as a bona fide meal pe riod, “[t]he employee must be completely relieved from duty for the purposes of eating re gular meals,” and “[t]he employee is not27 relieved if he is required to perform any dutie s, whether active or inactive, while eating.” Id. Most courts, however, apply the predominan t-benefit test to determine whether a meal period is bona fide. See, e.g. , Reich v. S. New Eng. Telecomms. Corp. , 121 F.3d 58, 65 (2d Cir. 1997) (The “predominant benefit st andard sensibly integrates developing case law with the regulations’ language and purpos e, and more importantly, with the language of the FLSA itself.” (citation and in ternal quotation marks omitted)); Babcock v. Butler Cty. , 806 F.3d 153, 15 6 (3d Cir. 2015); Roy v. Cty. of Lexington, S.C. , 141 F.3d 533, 545 (4th Cir. 1998); Hartsell v. Dr. Pepper Bottling Co. of Tex. , 207 F.3d 269, 274 (5th Cir. 2000); Ruffin v. MotorCity Casino , 775 F.3d 807, 811 (6th Cir. 2015); Leahy v. City of Chi., Ill ., 96 F.3d 228, 230 n.2 (7th Cir. 1996); Guyton v. Tyson Foods, Inc. , 767 F.3d 754, 763 (8th Cir. 2014); Beasley v. Hillcrest Med. Ctr., 78 F. App’x 67, 69–70 (10th Cir. 2003)

. But see Brennan v. Elmer’ s Disposal Serv., Inc., 510 F.2d 84, 88 (9th Cir. 1975) (applying a completely-relieved-from-duty te st under which “[a]n employee cannot be docked for lunch breaks during which he is required to continue with any duties related to his work” (emphasis added)). “The predom inant benefit test[ ] asks whether the [employee] is primarily engaged in work -related duties during meal periods.” Babcock , 806 F.3d at 156 (internal quotation marks om itted). If so, the employer must compensate the employee for the entire meal period. See Ruffin , 775 F.3d at 811. “But as long as the employee can pursue his or her mealtime adequa tely and comfortably, is not engaged in the performance of any substantial duties, an d does not spend time predominantly for the28 employer’s benefit, the employee is relieved of duty and is not entitled to compensation under the FLSA.” Id. (internal quotation marks omitted). On appeal, Plaintiffs do not contest that their meal break was a bona fide meal break. They challenge only the failure of the district court to compensate them for what they claim to be work performed during the break—donning, doffing, and walking. They contend that the district court denied comp ensation for the contested time on the ground that the predominant purpose of the meal brea k was to benefit the employees. If the court had rejected compensation on that ground, Pl aintiffs might have a convincing argument. But that is not how we read the court’s deci sion. It discussed the predominant-benefit test only to resolve whet her the meal break was a bona fide meal break. That discussion was necessary because Plaintiffs had argued (o r at least the court t hought that they had argued) that the break was not bona fide so Plaintiffs were entitle d to compensation for all 30 minutes. After finding the meal break to be bona fide, the court examined whether the plug times for the meal break were adeq uate to compensate fo r work time during the break. It found that Plaintiffs had not met th eir burden of showing th at the plug times for that period were inadequate. Pl aintiffs have not challenged that ruling. And they would fail if they did.
III. CONCLUSION For the foregoing reasons, we AFFIRM the district court’s judgment.