"A waiver is the intentional relinquishment of a known right. There must be both knowledge of the existence of the right and an intention to relinquish it." Pantle v. Indus. Comm'n, 335 N.E.2d 491, 496 (Ill. 1975); Vaughn v. Speaker, 533 N.E.2d 885, 890 (Ill. 1988); Sexton v. Smith, 492 N.E.2d 1284, 1287 (Ill. 1986). Put another way, "[i]f [the plaintiff] has intentionally relinquished a known right, either expressly or by conduct inconsistent with an intent to enforce that right, he has waived it and may not thereafter seek judicial enforcement."

In the present case there was no testimony by the claimant, and there was no other evidence that the respondent made any misrepresentation of fact. The claimant does not assert that she was ignorant of the existence of a time limitation on the filing of claims, or that the respondent failed to advise her of such. An omission of the latter sort, under the decision in Pantle v. Industrial Com. (1975), 61 Ill.2d 365, would, of course, not in itself create an estoppel. What the claimant relies on here are statements made to her by several of the respondent's employees, to whom she spoke at various times in 1971, that the respondent would "take care" of her.

Consequently, Byron is not precluded, as a matter of law, from showing that it reasonably relied on the alleged stand-still agreement with Dunham. • 9 Having decided the certified questions favorably to Byron, we need only further note that estoppel is ordinarily a question of fact, to be determined by the trier of fact ( Lawrence v. Board of Education of School District 189 (1987), 152 Ill. App.3d 187, 201). Only where there is no dispute as to the material facts, and only one inference can be drawn from the facts, does estoppel become a question of law. ( Pantle v. Industrial Comm'n (1975), 61 Ill.2d 365, 369.) However, if the facts are contested or if reasonable minds might draw different inferences from undisputed evidence, estoppel becomes a question of fact. Pantle, 61 Ill.2d at 369.

• 10, 11 Waiver, the intentional relinquishment of a known right, can arise either expressly or by conduct inconsistent with an intent to enforce the right. ( Pantle v. Industrial Comm'n (1975), 61 Ill.2d 365, 372, 335 N.E.2d 491, 496; Phillips v. Elrod (1985), 135 Ill. App.3d 70, 74, 478 N.E.2d 1078, 1082.) Where there is no dispute as to the material facts and only one reasonable inference can be drawn therefrom, it is a question of law whether the facts proved constitute waiver.

This court has held that an employer's failure to advise a claimant of the statute of limitations for filing a workers' compensation claim does not, in and of itself, create an estoppel. City of Chicago v. Industrial Comm'n, 75 Ill.2d 270 (1979); Pantle v. Industrial Comm'n, 61 Ill.2d 365 (1975). We adhere to this court's prior holdings and reject the claimant's argument.

In this regard we must point out that "equitable estoppel" and "waiver" are two distinct concepts, though they have similarities and are sometimes used interchangeably. A waiver is a voluntary relinquishment of a known right, claim or privilege ( Pantle v. Industrial Comm'n (1975), 61 Ill.2d 365), whereas an equitable estoppel may arise even though there was no intention on the part of the party estopped to relinquish any existing right. Moreover, prejudice to the other party is one of the essential elements of an equitable estoppel, whereas a waiver does not necessarily imply that the party asserting it has been misled to his detriment. (See generally 28 Am.Jur.2d Estoppel Waiver § 30 (1966).)

No claim was filed until November 1972, about 21 months later. In Pantle v. Industrial Com. (1975), 61 Ill.2d 365, as in this case, there was an extended delay in filing a claim. The claimant took no steps to ascertain if a written claim had to be filed to collect compensation.

A statute of limitations is an affirmative defense that may be waived by the parties and is open to pleas of estoppel. Pantle v. Industrial Comm'n, 61 Ill.2d 365, 367 (1975). In workers' compensation cases, statutes of limitations are designed to assure fairness to employers by protecting against claims that are too old to be successfully investigated and defended.

The claimant's position is that the circuit court properly ruled that the employer is estopped from asserting the statute of limitations because the claimant relied on the acts and representations of the insurance company to his detriment and had no way of knowing the true facts. (See Pantle v. Industrial Comm'n (1975), 61 Ill.2d 365, 335 N.E.2d 491.) The acts and representations of the insurance company which the claimant argues that he was misled by were that the settlement offer was guaranteed, that the parties agreed to a final medical examination to determine if more surgery was needed, and that the offer would remain open until after the medical evaluation was completed.

Schmidt v. Landfield (1960), 20 Ill.2d 89, 94; MBC, Inc. v. Space Center Minnesota, Inc. (1988), 177 Ill. App.3d 226, 230-31. • 7 Generally, questions of waiver and estoppel are for the trier of fact. ( Aetna Casualty Surety Co. v. Oak Park Trust Savings Bank (1988), 168 Ill. App.3d 1000, 1004.) If the facts necessary to constitute either waiver or estoppel are in dispute or if reasonable minds might differ as to the inferences to be drawn from the facts in evidence, then both issues become questions of fact. ( Pantle v. Industrial Comm'n (1975), 61 Ill.2d 365, 369.) Where there is no dispute as to the material facts and only one reasonable inference can be drawn therefrom, it is a question of law whether the facts proved constitute estoppel.