PUBLISH UNITED STATES CO URT OF APPEALS FOR THE TENTH CIRCUIT

__________________ _______________ SAMANTHA HALL,
Pl aintiff - Appellant,

v. CONOCO INC.; CONOCOPHILLIPS COMPANY; PHILLIPS 66 COMPANY,
De fendants - Appellees. No. 17-6086

__________________ _______________ Appeal from the United States District Court for the Western District of Oklahoma (D.C. No. 5:14-CV-00670-HE)

__________________ _______________ Jason B. Aamodt of Indian & Environmental Law Group, PLLC, Tulsa, Oklahoma (Krystina E. Phillips, Dallas L.D. Strimple, of Indian & Environmental Law Group , PLLC, Tulsa, Oklaho ma; Trae Gray, Ryan Ellis, of LandownerFirm, PLLC, Coalga te, Oklahoma; G. Steven Stidham of Levinson, Smith & Huffman, P.C., Tulsa, Oklahoma, with him on the briefs), for Plai ntiff-Appellant. Brett J. Young (Joy M. So loway, Katherine D. Ma ckillop, Devin Wagner, with him on the brief), of Norton Rose Fulbright US LLP, Houston, Texas, for Defendants-Appellees.

__________________ _______________ Before BACHARACH , MURPHY , and McHUGH , Circuit Judges.

__________________ _______________ BACHARACH , Circuit Judge.

__________________ _______________ FILED United States Court of Appeals Tenth Circuit 

### April 10, 2018
Elisabeth A. Shumaker Clerk of Court2 This appeal involves issues of causation and exclusion of expert testimony. These issues arose in a suit by Ms. Sama ntha Hall against Conoco Inc., ConocoPh illips Company, and Phillips 66 Company (collectively, “ConocoPhillips”) on theories of negligence, negligence per se, and strict liability. Ms. Hall was diagnosed with leukemia, and she attributes the disease to a ConocoPhillips refinery’s emissi ons of a chemical known as benzene. Liability turned largely on whether benzene emissions had caused Ms. Hall’s leukemia. On the issue of caus ation, the district court excluded testimony from two of Ms. Hall’s expe rts and granted su mmary judgment to ConocoPhillips. We affirm because

 the district court did not abuse its discretion in excluding the expert testimony and

 expert testimony was necessary to create a genuine issue of material fact on causation b ecause of the le ngth of time between the exposure to benzene and the onset of Ms. Hall’s disease. I. Background As a child, Ms. Hall had lived near ConocoPh illips’s refinery in Ponca City, Oklahoma. R oughly two decades later, Ms. Hall developed a form of leukemia known as “Acute Myeloid Leukemia with Inversion 16.” This disease, according to Ms. Hall, resulted from her early exposure to the refinery’s emissions of benzene.3 In district court, Ms. Hall tried to prove this link through three expert witnesses:
1. Dr. David Mitc hell, an air modeler,
2. Dr. Steven Gore, an oncologist, and
3. Dr. Mary Calvey, an epidemiologist. Dr. Mitchell created an air model to estimate benzene concentrations near where Ms. Hall had lived. Based on Dr. Mitchell’s estimates, Dr. Gore

 calculated Ms. Hall’s cumulativ e exposure to benzene and

 used this calculation to opine that ben zene exposure had caused Ms. Hall’s leukemia. Dr. Calvey expressed a similar opinion. ConocoPhillips moved for

 exclusion of opinion testimony by multiple expert witnesses, including Dr. Gore a nd Dr. Calvey and

 summary judgment on the issue of causation. The district court grante d the motion to exclude th e expert testimony by Drs. Gore and Calvey. In the absence of their te stimony, the court also granted summary judgment to ConocoPhillips, conc luding that Ms. Hall had not presented sufficient eviden ce linking her di sease to benzene
exposure. II. Exclusion of Expert Testimony Ms. Hall challenges th e district court’s exclusion of expert testimony by Drs. Gore and Calvey. We reject this challenge.4 A. Standard of Review The district court has “wide latitud e” in deciding wh ether to exclude expert testimony, and we review the manner in which the district court exercises this gatekeeping functi on for an abuse of discretion. Bitler v. A.O. Smith Corp. , 400 F.3d 1227, 1232 (10th Cir. 2005). The district court’s exclusion of expert testimony is governed by federal law. See Sims v. Great Am. Life Ins. , 469 F.3d 870, 879 (10th Cir. 2006). Under Federal Rule of Evidence 702, a qualified expert witness may give opinion testimony if

 the expert’s scientific knowledg e would help the fact-finder understand the evidence,

 “the testimony is based on sufficient facts or data,”

 “the testimony is the product of reliable principles and methods,” and

 “the expert has reliably applied the principles and methods to the facts of the case.” Fed. R. Evid. 702. Before expert testimony can be admitted, the dist rict court must determine that th e proposed testim ony is reliable. Daubert v. Merrell Dow Pharm. , 509 U.S. 579, 589 (1993). The di strict court’s assessment of reliability is reviewed for an abuse of discretion. Goebel v. Denver & Rio Grande W. Ry. , 346 F.3d 987, 990 (10th Cir. 2003). This review includes consideration of whethe r “the reasoning and me thodology underlying the5 expert’s opinion . . . is both scientifically va lid and applicable to a particular set of facts.” Id. at 991.
B. Dr. Gore’s Testimony Dr. Gore rendered a differential di agnosis on the cause of Ms. Hall’s leukemia. A differential di agnosis “rule[s] in all scientifically plausible causes of the injury and then rule[s] out the least plausible causes until only the most likely cause remain[s].” Id. at 990. Dr. Gore’s first step was to rule in benzene, smokin g, and idiopathic causes as potential causes of Ms. Hall’s leukemia. 1 Dr. Gore then ruled out smoking as a potential cause, leading him to conclude that benzene exposure had caused Ms. Hall’s leukem ia. Dr. Gore did not expressly rule out the possibility of idiopathic causes. The district court assumed that a differential diagnosis could provide a suitable methodology. Bu t the district court regarded Dr. Gore’s differential diagnosis as unreliable ba sed partly on his failure to justify ruling in benzen e or ruling out “idi opathic causes” of Ms. Hall’s disease. Hall v. ConocoPhillips , 248 F. Supp. 3d 1177, 1190-91 (W.D. Okla. 2017) (quoting Chapman v. Procter & Gamble Distrib. , 766 F.3d 1296, 1311 (11th Cir. 2014)). This reas oning fell within the dist rict court’s discretion.

1 Dr. Gore and other experts explained that an “idiopathi c” disease is a disease in which the cause is unknown.6 1. Ruling In Benzene To use a differential diagnosis, Dr. Gore needed to consider whether he could rule in benzene as a poten tial cause of Ms. Ha ll’s disease. We may assume, as the district court di d, that benzene em issions can cause Acute Myeloid Leukemia w ith Inverse 16. With th is assumption, however, Ms. Hall would still have needed to show that the benzene emissions actually caused her disease. For this showing, Ms. Hall relied on Dr. Gore’s quantification of the exposure to benzene. To quantify the exposure, Dr. Gore used the work of another expert witness, Dr. Mitchell, who had constr ucted an air mode l to estimate the highest hourly average conc entration of benzene. W ith this estimate, Dr. Gore quantified the cumulative exposu re to benzene based on how long Ms. Hall had lived near the refinery. 2 The result led Dr. Gore to rule in benzene as a potential cause of Ms. Hall’s leukemia. The district court found two flaws in this methodology:
1. Dr. Gore could not reliably use the high est hourly averageemission level to calculate Ms. Hall’s cumulative exposure to benzene.

2 Dr. Gore later upped his estimate of Ms. Hall’s tota l exposure based on new air modeling by Dr. Mitchell, which in turn had been based on new information. The supplemental estimat es of Drs. Mitche ll and Gore were excluded in district cour t based on a failure to timely disclose these estimates. The parties dispute the corr ectness of this ruling, but we need not reach the issue because we affirm the exclusion of Dr. Gore’s opinion based on flaws in his methodology. The newly ac quired information did not affect these flaws.7 2. Dr. Gore’s calculation was base d on mistakes involving the extent of Ms. Hall’s exposure to benzene. In finding these flaws, the district court acted within its discretion. a. The Choice of the Highest Hourly Average-Emission Level Dr. Gore estimated Ms. Hall’s cumu lative exposure by taking one of Dr. Mitchell’s figures (the highes t hourly average-em ission level). ConocoPhillips questions the use of this figure, pointing ou t that Dr. Gore could have used other figures from Dr. Mitchell’s air model. In this model, Dr. Mitchell had estimated benzene emissions over an extended time period. This estimate included the highest hourly average concentration of benzene while Ms. Hall lived near the refinery. Dr. Mitchell took this figure and instructed Dr. Gore to use it for his own calculation. But Dr. Mitchell admitt ed that he was not qua lified to decide which figure to use in assessing the impact of benzene emissions on human health: Q. You are not qualified when it comes to analyzing what value—acute, chronic, subchronic—is more relevant for assessing human health risk for benzene or any other chemical. You are not qualif ied to offer that opinion. A. I fully agree with that. I’m an air modeler and I’m a meteorologist.

. . .8 Q. And you don’t know which one of those matters most or matters at all for assessing wh ether or not Samantha Hall developed [acute myeloid leukemia] from benzene? A. Counselor, that’s out of my expertise. I’m not—I’m an air modeler and a meteorologist. Appellant’s App’x at 4944-45 . Dr. Mitchell conceded that selection of the concentration level was best left to an oncologist like Dr. Gore. 3 In turn, Dr. Gore acknowledged that he had not independ ently chosen which figure to use. Instead, he had admittedly relied on Dr. Mitche ll’s expertise to select the pertinent figure. Dr. Gore testified that he had called Dr. Mitchell, who provided assurance that the highest hourly aver age-emission level was the metric used in the industry. Appellant’s App’x at 5162

. The district court could reasonably consider this assurance an inadequate safeguard of reliability. See Mitchell v. Gencorp Inc. , 165 F.3d 778, 781 (10t h Cir. 1999) (“The expert’s assurance that the methodol ogy and supporting data is reliable will not suffice.”). Without an adequate safeguard of reliability, the district court could reasonably conclude that neither Dr. Gore nor Dr. Mitchell could defend the use of the highest hourly average-emission level. Both e xpert witnesses

3 Dr. Mitchell noted that he was conf ident in his choice of the highest hourly average because this was the figure that other expert witnesses had always requested. But requests from ot her expert witnesse s do not obviate the need for someon e with expertise to select the appropriate concentration level for Dr. Gore’s calculation.9 had seemingly disclaimed any responsibility for picking this figure: Dr. Mitchell had regarded Dr. Gore as th e expert and Dr. Gore had regarded Dr. Mitchell as the expe rt, leaving no one qualifi ed to choose which concentration level to use. This circular loop stirred broade r concern over th e entirety of Dr. Gore’s calculation. That calculation was designed to estimate Ms. Hall’s cumulative exposure to be nzene. If Dr. Gore had calculated the cumulative exposure based on an incorrect figure, the cour t could reasonably question the decision to ru le in benzene as a potential cause. 4 As a result, we conclude that the district court acted within its di scretion in questioning the reliability of Dr. Gore ’s decision to use the highes t hourly averageemission level. b. Dr. Gore’s Errors and Inconsistencies Regarding the Extent of Ms. Hall’s Expo sure to Benzene The district court also identified three of Dr. Gore’s errors and inconsistencies about the extent of Ms. Hall’s exposure to benzene. First, Dr. Gore assumed that Ms. Hall had lived near the refinery for eight years. But Dr. Gore was mist aken; Ms. Hall had lived near the refinery for only about four years. As Dr. Gore acknowledged, this error

4 Ms. Hall argues that medical doctor s can rely on expert air modelers. Ms. Hall is correct, and the district court never suggested otherwise. The problem was that no one had justified the selection of th e figure that was used in calculating Ms. Hall’s cumulative exposur e to benzene.10 meant that his estimate of the cumulative expo sure was roughly double what it should have been. Second, Dr. Gore v acillated on his own me thodology. He initially stated that he had calculat ed Ms. Hall’s exposure by

 using the highest hourly averag e-emission level from Dr. Mitchell’s model and

 assuming that Ms. Hall had been exposed to that level for one hour every day. But in a later declaration, Dr. Gore stated that he had assu med exposure for 8 hours per day, 5 days per week, 50 weeks per year. At a hearing, Dr. Gore switched back, testifying that hi s declaration had be en mistaken and that he had actually assumed on ly one hour of e xposure per day. Third, the district court found th at Dr. Gore had b een inconsistent about what he was calcula ting. He sometimes said that he was calculating Ms. Hall’s exposure to benzene; othe r times, however, he stated that he was calculating exposure to vo latile organic compounds. These inconsistencies mattered because benz ene is only one of many volatile organic compounds. 5

5 In his deposition, Dr. Gore estimat ed Ms. Hall’s exposure to benzene as only 20% of her broa der exposure to volatil e organic compounds. But Dr. Gore later backtracked, stating that his initial cal culation had been solely for benzene and had excluded other vola tile organi c compounds.11 In light of these errors and inconsistencies, the district court could reasonably questi on the reliability of Dr. Gore ’s opinion ruli ng in benzene exposure as a pote ntial cause. 2. Ruling Out Idiopathic Causes Even if benzene could be ruled in as a potential cause, Dr. Gore’s differential diagnosis wo uld have depended on hi s ability to ru le out less plausible causes of Ms. Hall’s disease. The district court concluded that Dr. Gore had failed to rule out idiopathic causes, and this conclusion fell within the district court’s discretion. The parties agreed that acute myeloid leukemia is frequently caused by idiopathic sources. For example, Ms. Hall presented expert testimony that 70-75% of cases of acute myeloid leukemia are idiopathic. And Dr. Gore agreed that acute my eloid leukemia is ordinari ly idiopathic in origin. The resulting question is whether Dr. Go re needed to cons ider and rule out idiopathic causes. The distri ct court answered “yes.” A differential diagnosis is designed to identify the mo st likely cause of a disease. See Goebel v. Denver & Rio Grande W. Ry. , 346 F.3d 987, 990-91 (10th Cir. 2003). An expert ne ed not consid er and rule out every conceivable cause. See Bitler v. A. O. Smith Corp. , 400 F.3d 1227, 1238 n.6 (10th Cir. 2005); accord Best v. Lowe’s Home Ctrs. , 563 F.3d 171, 181 (6th Cir. 2009) (“[D ]octors need not rule out every conceivable cause in order for their differential-diagnosis-based opinions to be admissible.”).12 But the expert must still consider all plausible causes and rule out the less plausible ones until only the most like ly cause remains. See Glastetter v. Novartis Pharm. , 252 F.3d 986, 989 (8th Cir. 2001); see also Hollander v. Sandoz Pharm. , 289 F.3d 1193, 1211- 12 (10th Cir. 2002 ) (noting that a reliable differential diagnosis eliminates “all other possible causes of the victims’ condition . . . leaving only the toxic substance as the cause” (quoting Turner v. Iowa Fire Equip. , 229 F.3d 1202, 1209 (8th Cir. 2000))). Dr. Gore did not rule out the possibility of an idiopathic cause for Ms. Hall’s acute myeloid leukemia. This omission concerned the district court because the evidence had pointed to idiopathic causes in most cases of acute myeloid leukemia , and the district court could reasonably view the failure to rule out idiopathic causes as a fatal error tainti ng the differential diagnosis. See Milward v. Rust-Oleum Corp. , 820 F.3d 469, 476 (1st Cir. 2016) (upholding exclusion of expert testimony based on a differential diagnosis, reasoning that it was unreliable to link benzene to acute promyelocytic leukemia in part because the diseas e has an extraordinary number of idiopathic cases); see also Chapman v. Procter & Gamble Distrib. , 766 F.3d 1296, 1311 ( 11th Cir. 2014) (holding that a failure to consider idiopathic causes rendered the differential dia gnosis unreliable); Tamraz v. Lincoln Elec. , 620 F.3d 665, 675 (6th Cir. 2010) (holding that expert testimony regarding causation of a given disease was inadmissible13 because “the vast major ity of . . . cases” invol ve “unknown (i diopathic) causation,” “making it impossible to ignore and rule out”); accord Blanchard v. Goodyear Tire & Rubber Co. , 30 A.3d 1271 , 1275-76 (Vt. 2011) (stating that the pres ence of a known risk fact or is not sufficient to rule out idiopathic origin, particularly when most incide nts of the disease lacked a known cause). Ms. Hall responds wi th two arguments: 1. The district court misunderst ood the concept of “idiopathic” causes. 2. The Tenth Circuit does not require diff erential diagnoses to rule out idiopathic causes. We reject both arguments. First, Ms. Hall argues that the di strict court misund erstood the term “idiopathic.” She character izes “idiopathic” as a diagnosis by exclusion: only if all known factors are ruled out, leaving no known plausible factors, can the leukemia be cons idered idiopathic. Under this view, it is illogical to ask Dr. Gore to “rule out” idiopa thic causes because a disease can be considered idiopathic only if all identi fiable causes have been ruled out. Based on this definition of “idiopat hic,” Ms. Hall regards the district court’s reasoning as faul ty. To Ms. Hall, Dr. Gore properly ruled in all known risk factors and rule d out the implausible ones until he was left only with benzene. Because benzene rema ined a plausible cause, the term “idiopathic” would not fit.14 But the district court could reasonably take a different approach when analyzing “idiopathic” causes. One can regard “idi opathic” causes as recognition of the medica l community’s in ability to identify all of the causes of a disease. See Tamraz v. Lincoln Elec. , 620 F.3d 665 , 668 (6th Cir. 2010) (stating that th e term “idiopathi c” is “another wa y of saying the medical community does not know why a given individual has the disease”); Huss v. Gayden , 571 F.3d 442, 459 (5th Cir. 2009) (indicating that a condition is “idi opathic” when “the medi cal community has a poor understanding of wh at causes it”); see also Vacuum De positing, Inc. v.
Dever , 285 S.W.3d 730, 733 (Ky. 2009) (“ In common parlance, the term ‘idiopathic’ means ‘arisi ng spontaneousl y or from an obscure or unknown cause.’” (footnote omitted)). Because idiopathy accounts for more than half of the cases of acute myeloid leukemia, a differential diagnosis could be considered inherently unreliable here. See Tamraz , 620 F.3d at 675 (“ [U]nknown (idiopathic) causation . . . currently accounts for the vast ma jority of Parkinson’s Disease cases, making it impossible to ignore and difficult to rule out.”); Bland v. Verizon Wireless, (VAW) , 538 F.3d 893, 897 (8th Cir. 2008) (“Where the cause of th e condition is unknown in th e majority of cases, [the expert witness] ca nnot properly conclude, based upon a differential diagnosis, [the plaintiff’s] exposure to freon was ‘the most probable cause’ of [the plaintiff’s] exer cise-induced asthma.”); see also Restatement15 (Third) of Torts: Liab. for Physical and Emotional Harm § 28 cmt. c(4) (Am. Law. Inst. 2010) (“Wh en the causes of a di sease are largely unknown, . . . [a differential diagnosis] is of little assistance.”). Given the predominance of idiopathic causes, we conclude that the district court had the discretion to consider Dr. Gore’s differential diagnosis unreliable. Second, Ms. Hall contends that the Tenth Circuit does not require experts to rule out idiopathic causes in conducting a differential diagnosis. For this contention, Ms. Hall relies on Bitler v. A.O. Smith Corp. , 400 F.3d 1227 (10th Cir. 2005). Ms. Hall has misinterpreted Bitler . There we observed that an expert need not “‘ categorically exclude each and every possible alternative cause.’” Bitler , 400 F.3d at 1238 n.6 (quoting Stephen A. Saltzburg et al., Federal Rules of Evidence Manual 702-33 (8th ed. 2002)). This observati on does not preclude a district court from questioning the reliabilit y of a differential diagno sis when the cause of a disease is unknown most of the time.
* * * The district court could justifiably regard Dr. Gore’s differential diagnosis as unreliable because of his failure to (1) justify ruling in benzene or (2) rule out id iopathic causes. Thus, the district court did not abuse its discretion in excluding Dr. Gore’s opinion based on his differential diagnosis.16 C. Dr. Calvey’s Testimony The district court also excluded Dr. Calvey’s opinion testimony linking benzene to Ms. Hall’s diseas e. Like Dr. Gore, Dr. Calvey conducted a differential diagnosis and opined that benzen e had caused Ms. Hall’s leukemia. This opinion was excl uded in part because Dr. Calvey had not “adequately address[ed] the issue of exposure.” Hall v. ConocoPhillips , 248 F. Supp. 3d 1177, 1193 (W.D. Ok la. 2017). Ms. Hall does not challenge this rationale, foreclosing reversal of the exclusion of Dr. Calvey’s testimony. See Bones v. Honeywell Int’l , 366 F.3d 869 , 877 (10th Cir. 2004) (affirming a grant of summ ary judgment becau se the appellant failed to appeal an alternat ive basis for the ruling). III. Summary Judgment Ms. Hall challenges no t only the exclusion of expert testimony but also the grant of summary judgment to ConocoPhil lips. The district court concluded that without the expert te stimony by Dr. Gore and Dr. Calvey, Ms. Hall lacked the required eviden ce linking her disease to benzene emissions. Ms. Hall challenges th is conclusion, ar guing that the circumstantial evidence was enough to avoid summary judgment. 6

6 Both parties fo cus on Oklahoma law. Although federal law governs whether Ms. Hall presente d sufficient evidence of causation to defeat summary judgment, state law governs “what theories of causation are permissible and the general means permitted to establish causation.” Tingey v. Radionics , 193 F. App’x 747, 760 (10th Cir. 2006)17 We engage in de novo review of the grant of su mmary judgment. United States v. Turley , 878 F.3d 953, 956 (10th Cir. 2017). Summary judgment is appropriate only if the movant has shown

 the absence of a genuine issu e of material fact and

 the movant’s entitlemen t to judgment as a matter of law. Gutteridge v. Oklahoma , 878 F.3d 1233, 1238 (10th Cir. 2018). For causation, Ms. Hall points to circ umstantial evidence such as the presence of hydrocarbon le aks and odors in her neighborhood, groundwater contamination, a high benzene reading near her residence, and estimates by the Environmental Protection Agency showing increased risk from the refinery. This circumstantial evidence fails to create a genuine issue of material fact on causation because of the need for

 expert testimony on the link between her disease and benzene exposure and

 quantification of Ms. Hall’s exposure to benzene. A. The Necessity of Expert Testimony Ms. Hall’s circumstantial evidence does not create a genuine issue of material fact on causat ion because of the length of time between her exposure to benzene emissions and the onse t of her disease. (unpublished); see Wackman v. Rubsamen , 602 F.3d 391, 400 (5th Cir. 2010). The resolution of Ms. Hall’s cl aim depends on whet her the type of evidence submitted constitut ed a permissible means of proving causation. Thus, we apply state law. See Tingey , 193 F. App’x at 760, 764; Wackman , 602 F.3d at 400 & n.2.18 Oklahoma law gene rally requires expert tes timony for complex issues of medical causation. See, e.g. , Christian v. Gray , 65 P.3d 591, 601-02 (Okla. 2003) (“When an in jury is of a nature requiring a skilled and professional person to determine cause and th e extent thereof, the scientific question pres ented must necessarily be determined by testimony of skilled and professional persons.”); Ruland v. Zenith Constr. , 283 P.2d 540, 541 (Okla. 1955) (notin g that the cause of an illness “is a matter of medical science to be established by expert testimony”). An exception exists “w here the common knowledg e or experience of laymen is extensive enough to recognize or infer ne gligence from the facts . . . with reason able certainty.” Boxberger v. Martin , 552 P.2d 370, 373 (Okla. 1976). But the district court could reasonably c onclude that the long-term carcinogenic effects of benzen e exposure lie out side the ken of common experience, requ iring expert testimony. See Jones v. Ortho Pharm. Corp. , 163 Cal. App. 396, 403 (1985) (sta ting that the et iology of cancer lies “beyond the expe rience of laymen and can only be explained through expert testimony”). In light of the need for expert te stimony on the e ffects of benzene exposure, Ms. Hall could not avoid summary judgment by relying solely on circumstantial evidence linking her disease to benzene emissions.19 B. Quantification of Exposure to Benzene When causation involves a link between a disease and exposure to a toxin, the exposure must ordinarily be quantified. See Mitchell v. Gencorp,
Inc. , 165 F.3d 778, 781 (10th Cir. 1999) (“‘Sci entific knowle dge of the harmful level of exposure to a chemical plus know ledge that plaintiff was exposed to such quanti ties are minimal facts n ecessary to sustain the plaintiff’s burden in a to xic court case.’” (quoting Allen v. Pa. Eng’g , 102 F.3d 194, 199 (5 th Cir. 1996))). Thus, Ms. Hall’ s theory requi red not only expert testimony but also quantification of her exposure to benzene. See Twyman v. GHK Corp. , 93 P.3d 51, 59-60 (Okla. Civ. App. 2004) (faulting an expert for his inability to iden tify the presence of a chemical at sufficient levels to ha ve caused the injury). Ms. Hall disputes the need to quantify her expo sure. For this argument, Ms. Hall relies on Christian v. Gray , 65 P.3d 591 (Okla. 2003). There the plaintiffs asse rted that they had become sick from inhaling airborne chemicals at a circus. Id. at 594. The Oklaho ma Supreme Court concluded that the plaintiffs had not ne eded to quantify their exposure to the airborne chemical , reasoning that

 this approach would “prevent many lawsuits based upon a single-event exposure , such as, for exampl e, when a plaintiff brings an action and testifies of being enveloped by a great cloud of noxious gas from a calamitous event” and

 “‘evidence of instantaneous onse t of injury following a certain occurrence and expert testimony that the injury could have20 been caused by the oc currence’” is enough to survive summary judgment. Id. at 606 (quoting Martin v. Stratton , 515 P.2d 1366, 1371 (Okla. 1973)).
In Christian , the court concluded that quantitative measurement is sometimes unnecessary when the plai ntiff is exposed to an excessive amount of a chemical, fo llowed quickly by th e onset of symptoms. See id. Our case is far different . Ms. Hall alleges long-term exposure to benzene, causing leukemia decad es later. Thus, the Christian exception has no bearing here.
* * * To avoid summary judg ment on the issue of causation, Ms. Hall needed both expert te stimony and quantificatio n of her exposure to benzene. Without the propo sed testimony by Dr. Go re and Dr. Calvey, Ms. Hall lacked both the requ ired expert testimony a nd a way to quantify her exposure to benzene emissi ons. Accordingly, the district court did not err in granting summa ry judgment to Conoco Phillips on causation. IV. Conclusion We conclude that the district court did not err

 in excluding the testimony of Drs. Gore and Calvey and

 in concluding that ConocoPh illips was entitled to summary judgment on causation. Therefore, we affirm.